238 Nouns That Start with O [with Definitions and Examples]

To make one’s conversations and writings meticulous, professional and captivating, one should have a vast encyclopedia of nouns at one’s command, especially nouns that start with O. Memorizing a number of nouns beginning with O can prove to be a very fruitful step in achieving that goal. Nouns are important because they refer to places, objects and people and the more sophisticated abstract concepts. Without nouns, you will be left with verbs, adjectives and adverbs. The lack of nouns will eradicate any subject or object from your sentence which is as good as communication essentially nothing.

If you, as a reader, get hold of as many nouns starting with O as possible, you can build for yourself an impressive rapport among other speakers and writers. A list of nouns that start with O is provided in this article for your convenience. Now let’s go through the various categories of nouns provided in this article that also contains nouns that start with O to describe a person, place, and other abstract things. Learning nouns that start with O will not just help you in building your vocabulary but will also make you stand apart from the rest.

Table of Contents

Nouns That Start with O You Always Use

There are lots of nouns starting with O that we use on a regular basis in our writings and day-to-day oral communications. Nouns that start with O that one uses regularly are listed below.

1. Office

Definition: a room, set of rooms, or building used as a place for commercial, professional, or bureaucratic work
Synonyms: workplace, workroom
Example: I don’t leave the office until eight o’clock last night.

2. Orange

Definition: a round sweet fruit that has a thick orange skin and an orange center divided into many parts
Synonyms: citrus-fruits, tangerine
Example: Vitamin C is found in oranges and other citrus fruit.

3. Option

Definition: one thing that can be chosen from a set of possibilities
Synonyms: choice, preference, alternative
Example: The best option would be to cancel the trip altogether.

4. Object

Definition: a thing that you can see or touch but that is not usually a living animal, plant, or person
Synonyms: thing, item, body
Example: A new baby will automatically curl its fingers round any object it touches.

5. Observation

Definition: the act of observing something or someone
Synonyms: examination, consideration, investigation
Example: The police are keeping the suspect under observation.

6. Oxygen

Definition: a colorless, odorless reactive gas; the life-supporting component of the air
Synonyms: gas, air, oxygenation
Example: Oxygen is in high demand these days because of Covid-19.

7. Oil

Definition: a viscous liquid derived from petroleum, especially for use as a fuel or lubricant
Synonyms: lubricant, fuel, petrol

Example: Oil does not mix with water.

8. Omelet

Definition: a dish of beaten eggs cooked in a frying pan and served plain or with a savory or sweet topping or filling
Synonyms: scrambled-egg, frittata
Example: I’ll have an omelet with cheese on the side, please.

9. Outside

Definition: the outer part or side of something
Synonyms: exterior, surface
Example: The outside of the house needs painting.

10. Onion

Definition: a swollen edible bulb used as a vegetable, and composed of several concentric layers
Synonyms: shallots, allium cepa,
Example: Cook the onion in the oil until lightly colored.

Nouns That Start with O You Usually Use

With nouns, sentences are given more clarity as listeners would know what is the object or thing being mentioned and what is happening to that particular object or thing. Following is a list of nouns starting with O that we usually use in our daily life routine.

1. Origin

Definition: the point or place where something begins, or arises
Synonyms: beginning, start, origination
Example: There are many theories about the origin of life.

2. Opinion

Definition: a thought or belief about something or someone

Synonyms: viewpoint, angle, judgement
Example: What’s your opinion about this matter?

3. Oven

Definition: an enclosed compartment, usually part of a cooker, for cooking and heating food
Synonyms: stove, microwave, roaster
Example: She completely forgot the cake in the oven.

4. Operation

Definition: an act of surgery performed on a patient
Synonyms: surgery, incision, resection
Example: I’ve never felt better since my bypass operation.

5. Order

Definition: a request to make, supply, or deliver food or goods
Synonyms: command, request, instruction
Example: “Can I take your order now?” said the waiter.

6. Owner

Definition: a person who owns something
Synonyms: possessor, holder
Example: He and his sister are the owners of the restaurant.

7. Outfit

Definition: a set of clothes worn for a particular occasion or activity

Synonyms: costume, uniform, suit
Example: I’m going to wear my vampire outfit for Halloween.

8. Ornament

Definition: a thing used or serving to make something look more attractive but usually having no practical purpose
Synonyms: trinket, accessory, bibelot
Example: They spent decades collecting these colorful ornaments.

9. Officer

Definition: a member of the police force
Synonyms: agent, chief, deputy
Example: Two officers responded to the call at 282 Main Street.

10. Odor

Definition: a particular smell, especially a bad one
Synonyms: smell, aroma, stench
Example: The odor she had smelled earlier hung in the air.

Nouns That Start with O You Often Use

It’s difficult to write a sentence that does not include at least one noun. Following is a list of nouns starting with O that we often make use of.

1. Organization

Definition: a group of people who work together in an organized way for a shared purpose
Synonyms: company, firm, corporation
Example: The article was about the international aid organizations.

2. Oath

Definition: a serious promise that you will tell the truth or that you will do what you have said
Synonyms: pledge, vow, promise,
Example: Presidents take an oath to uphold the Constitution.

3. Offer

Definition: an expression of readiness to do or give something if desired
Synonyms: proposal, suggestion, proposition
Example: One day I’ll take you up on that offer.

4. Ounce

Definition: a very small amount of something
Synonyms: scrap, bit, iota

Example: Robyn summoned up every ounce of strength.

5. Objection

Definition: an expression or feeling of disapproval or opposition; a reason for disagreeing
Synonyms: complaint, grievance, protestation
Example: They have raised no objections to the latest plans.

6. Occasion

Definition: a particular time, especially when something happens or has happened
Synonyms: moment, event, circumstance
Example: We met on several occasions to discuss the issue.

7. Operator

Definition: someone who is skilled at dealing with people and getting what he or she wants from a situation
Synonyms: machinist, worker, dealer, arranger
Example: The tour operator will arrange transport and plan your itinerary.

8. Obesity

Definition: the condition of being very fat or overweight
Synonyms: fatness, stoutness, corpulence
Example: His obesity puts him at risk for major health problems.

9. Opening

Definition: a space or gap that allows passage or access
Synonyms: hole, aperture, gap

Example: An opening in the roof would get rid of the smoke.

10. Omen

Definition: something that is considered to be a sign of how a future event will take place
Synonyms: sign, foreshadowing, symbol
Example: Many people believe that a broken mirror is an omen of bad luck.

Nouns That Start with O You Sometimes Use

Nouns are very important for language development. They also enhance people’s overall expressive language. These are some of the nouns beginning with O that are not used on a regular basis in our daily life routine.

1. Obligation

Definition: an act or course of action to which a person is morally or legally bound
Synonyms: duty, commitment, responsibility
Example: I have an obligation to look after her.

2. Obstacle

Definition: a thing that blocks one’s way or prevents or hinders progress
Synonyms: The major obstacle to achieving that goal is money
Example: barrier, hurdle

3. Obsession

Definition: the state of being obsessed with someone or something
Synonyms: fixation, compulsion, fascination
Example: The kids have an obsession with computer games.

4. Offspring

Definition: children or young of a particular parent or progenitor
Synonyms: baby, kid, pup, children

Example: Tom’s sister came over on Saturday with all her offspring.

5. Organ

Definition: a part of the body of an animal or plant that performs a particular job
Synonyms: unit, part, structure
Example: He sustained injuries to his arms, legs and several internal organs.

6. Oration

Definition: a formal public speech about a serious subject
Synonyms: speech, address, lecture
Example: He asked for no funeral oration.

7. Organism

Definition: an individual animal, plant, or single-celled life form
Synonyms: being, creature, animal
Example: Amoebae and bacteria are single-celled organisms.

8. Oatmeal

Definition: meal made from ground oats, used in porridge or oatcakes
Synonyms: cereal, porridge

Example: I switched back to oatmeal for four days.

9. Oppression

Definition: the state of being subject to oppressive treatment
Synonyms: persecution, abuse, maltreatment
Example: Every human being has the right to freedom from oppression.

10. Orphanage

Definition: a home for children whose parents are dead or unable to care for them
Synonyms: asylum, shelter, foundation
Example: He donated 1,000 dollars to an orphanage.

Nouns That Start with O You Occasionally Use

Most of the noun words that start with O might be pretty commonly used, but there are some that are only used at some specific occasions. Following is a list of such nouns.

1. Oaf

Definition: a man who is rough or clumsy and unintelligent
Synonyms: clown, gawk, hulk
Example: They are just big, clumsy oafs.

2. Omnibus

Definition: a usually automotive public vehicle designed to carry a large number of passengers
Synonyms: bus, vehicle, tram
Example: In our neighborhood, most of the children ride an omnibus to school each day.

3. Onslaught

Definition: a fierce or destructive attack
Synonyms: charge, assault, attack
Example: It is unlikely that his forces could withstand an enemy onslaught for very long.

4. Opiate

Definition: a drug that contains opium, especially one that causes sleep
Synonyms: drug, narcotic, sedative
Example: One woman suffered such severe pain she had to take opiates to control it.

5. Optician

Definition: a person qualified to prescribe and dispense glasses and contact lenses, and to detect eye diseases
Synonyms: ophthalmologist, occulist
Example: Her youngest daughter is an optician.

6. Orgy

Definition: a period when there is too much of something, usually a bad or harmful activity
Synonyms: debauch, carouse, bacchanalia
Example: The protest degenerated into an orgy of looting and shooting.

7. Orient

Definition: the countries of East and Southeast Asia
Synonyms: east, exotic, muddle
Example: Is the Orient too foreign for you?

8. Ordnance

Definition: military supplies, especially weapons and bombs
Synonyms: guns, cannon, artillery
Example: The gun was a brand new piece of ordnance.

9. Osmosis

Definition: a spontaneous diffusion of water or other solvents through a semipermeable membrane
Synonyms: diffusion, infiltration
Example: Fluid flows back into the tiny blood vessels by osmosis.

10. Omnipotence

Definition: unlimited power and the ability to do anything
Synonyms: supremacy, pre-eminence
Example: America had illusions of omnipotence in the 1950s.

Nouns That Start with O You Seldom Use

While going through a written piece or while listening to a person talking, you often come across nouns that you haven’t heard of a lot. Below is a list of noun words that start with the letter O that are seldom used.

1. Obelisk

Definition: a tapering stone pillar, typically having a square or rectangular cross section, set up as a monument or landmark
Synonyms: pillar, monument, memorial
Example: Each obelisk listed the members of an immortal household and their offspring.

2. Ogre

Definition: a fierce and frightening person
Synonyms: monster, bogeyman, devil
Example: Some of my teachers were real ogres.

3. Oligarchy

Definition: government by a small group of powerful people
Synonyms: authoritarianism, autocracy, totalitarianism
Example: Their nation is an oligarchy.

4. Onyx

Definition: a valuable stone that is used in jewelry, with white, black, grey, and other colored stripes
Synonyms: stone, mineral, slab
Example: Has my story of that pearl and onyx been lost on you?

5. Opus

Definition: any work of art
Synonyms: composition, work, piece
Example: He showed us his latest opus, a truly magnificent painting of a vase of flowers.

6. Ornithology

Definition: the study of birds
Synonyms: science, zoology, research
Example: He found his vocation in ornithology.

7. Overalls

Definition: a loose-fitting coat or one-piece garment worn over ordinary clothes for protection against dirt or heavy wear
Synonyms: dungarees, outfit
Example: She put on some overalls and got out a tin of paint.

8. Osteopathy

Definition: the treatment of injuries to bones and muscles using pressure and movement
Synonyms: ministration, surgery
Example: Osteopathy involves massage and manipulation of the bones and joints.

9. Oxymoron

Definition: a figure of speech in which apparently contradictory terms appear in conjunction
Synonyms: opposites, juxtaposition
Example: The genre of ‘historical fiction’ is an oxymoron to begin with.

10. Onomatopoeia

Definition: the act of creating or using words that include sounds that are similar to the noises the words refer to
Synonyms: echo, repetition, imitation
Example: When asked to point out the onomatopoeia in the sentence describing a bird, I pointed to “chirp”.

Nouns That Start with O You Rarely Use

There are some O-nouns that are rarely seen or heard in both writing and communication. When a reader gets to know about them he is flabbergasted that such nouns even exist. Below are some of those nouns.

1. Obeisance

Definition: a gesture expressing deferential respect, such as a bow or curtsy
Synonyms: salutation, curtesy, bob
Example: She made a deep obeisance.

2. Opprobrium

Definition: harsh criticism or censure
Synonyms: vituperation, criticism, censure
Example: International opprobrium has been heaped on the country following its attack on its neighbors.

3. Oblation

Definition: something that is offered as a religious sacrifice
Synonyms: offering, sacrifice, libation
Example: Incense was used for purification and as an oblation to ancestors.

4. Obliquity

Definition: deviation from moral rectitude or sound thinking
Synonyms: shift, transgression, turning
Example: Barrow’s fade to winter blackness results from cosmic obliquity.

5. Obscurantism

Definition: the practice of deliberately preventing the facts or full details of something from becoming known
Synonyms: backsliding, backlash, withdrawal
Example: Religious prejudice and scientific obscurantism have been closely entangled.

6. Offertory

Definition: the offering of the bread and wine at the Eucharist
Synonyms: offering, allowance, benefit
Example: They donated the money to a collection which was brought up at the offertory.

7. Opulence

Definition: the quality of being expensive and luxurious
Synonyms: richness, luxury, splendor
Example: He says living in such opulence makes him uneasy.

8. Orifice

Definition: an opening or hole, especially one in the body, such as the mouth
Synonyms: opening, hole, aperture
Example: The driver was bleeding from every orifice.

9. Obloquy

Definition: very strong public criticism or blame
Synonyms: vilification, condemnation, denunciation
Example: His controversial essays have brought him much obloquy.

10. Oubliette

Definition: a secret dungeon with access only through a trapdoor in its ceiling.
Synonyms: dungeon, jail, cell
Example: Sarah ends up in an oubliette where she reunites with her husband.

Positive Nouns That Start with O

There are some positive nouns that both carry and spread positivity and also describe your skills, results, and accomplishments. These are some of the positive nouns that start with O that you should have at your disposal.

1. Optimist

Definition: a person who tends to be hopeful and confident about the future or the success of something
Synonyms: dreamer, hoper, fantast
Example: Only an eternal optimist could expect success.

2. Oasis

Definition: a fertile spot in a desert, where water is found
Synonyms: spring, wellspring
Example: They stopped for the night at an oasis.

3. Objective

Definition: something that you plan to do or achieve
Synonyms: aim, intention, purpose
Example: Her prime objective now is simply to stay in power.

4. Occupation

Definition: a job or profession
Synonyms: work, profession, job
Example: Please fill in your name, age, and occupation.

5. Odyssey

Definition: a long wandering or voyage usually marked by many changes of fortune
Synonyms: adventure, expedition, exploration
Example: They departed Texas on a three-year odyssey that took them as far as Japan

6. Obedience

Definition: compliance with an order, request, or law or submission to another’s authority
Synonyms: acquiescence, compliance
Example: Obedience is the first duty of a soldier.

7. Oomph

Definition: the quality of being exciting, energetic, or sexually attractive
Synonyms: fortitude, stamina, vigor
Example: You need to put some oomph into your acting.

8. Opportunity

Definition: a time or set of circumstances that makes it possible to do something
Synonyms: chance, occasion, moment
Example: Please contact us at the earliest opportunity.

9. Ovation

Definition: a sustained and enthusiastic show of appreciation from an audience, especially by means of applause
Synonyms: applause, clapping, cheering
Example: Her performance received a thundering ovation.

10. Overture

Definition: a piece of music that is an introduction to a longer piece, especially an opera
Synonyms: opening, introduction, prelude
Example: The programme opened with the overture to Wagner’s Flying Dutchman.

Nouns That Start with O – Full List (238 words)

Oaf
Oak
Oasis
Oath
Oathe
Oatmeal
Obedience
Obelisk
Obesity
Object
Objectification
Objection
Objective
Objectivity
Objector
Obligation
Oblige
Obliteration
Oblivion
Oblong
Oboist
Obscenity
Obscurity
Observance
Observation
Observer
Obsession
Obsidian
Obstacle
Obstructionist
Obverse
Ocarina
Occasion
Occlusion
Occupancy
Occupant
Occupation
Occurrence
Ocean
Oceanography
Ocelot
Ocher
Ochre
Octagon
Octahedron
October
Octopus
Octoroon
Ode
Odor
Odyssey
Oep
Offal
Offender
Offense
Offer
Offering
Offersey
Office
Officer
Official
Officialdom
Offing
Offshoot
Offspring
Ogre
Oil
Oilcloth
Oiliness
Oilseed
Ointment
Oiticica
Oleomargarine
Olive
Olympian
Ome
Omelet
Omen
Omission
Ommission
Omnipotence
Omnipotent
Omnivore
Oneupmanship
Onion
Onlooker
Onrush
Onset
Onslaught
Oodles
Ooh
Oomph
Ooze
Opal
Open
Opener
Opening
Openness
Opera
Operand
Operation
Operator
Operetta
Opinion
Opium
Opponent
Opportunism
Opportunity
Opposite
Opposition
Oppression
Opprobrium
Optimality
Optimism
Optimist
Optimization
Optimum
Option
Oracle
Oral
Orange
Oration
Orator
Oratorio
Oratory
Orb
Orbit
Orchard
Orchestra
Orchestration
Orchestrator
Ordeal
Order
Orderly
Ordinance
Ordinary
Ordnance
Organ
Organdy
Organification
Organism
Organist
Organization
Organizer
Orgone
Orgy
Orientation
Origin
Original
Originality
Origination
Originator
Ornament
Ornamental
Ornamentation
Orphan
Orphanage
Orthicon
Orthodontist
Orthography
Orthophosphate
Oscillation
Oscillator
Osmium
Ossification
Ostracism
Ostrich
Otter
Ounce
Ouster
Outback
Outbreak
Outburst
Outcast
Outcome
Outcry
Outfield
Outfielder
Outfit
Outflow
Outgrowth
Outhouse
Outing
Outlaw
Outlawry
Outlay
Outlet
Outline
Outlook
Outpatient
Outpost
Output
Outrage
Outreach
Outset
Outside
Outsider
Oval
Ovation
Oven
Overall
Overcast
Overcoat
Overestimation
Overexploitation
Overflow
Overhang
Overhaul
Overhead
Overlay
Overload
Overnight
Overpayment
Overpopulation
Overpressure
Overprotection
Overrun
Overseer
Oversight
Oversimplification
Overthrow
Overtime
Overture
Overweight
Owi
Owl
Owner
Ownership
Oxalate
Oxcart
Oxen
Oxidation
Oxide
Oxygen
Oxytetracycline
Oyster
Ozone

Final Thoughts on Nouns That Start with O

It is hoped that you would have learnt something new about the use of nouns while reading this article. There is a never-ending list of nouns and new nouns are being added to it every now and then. By having a large reservoir of nouns at your disposal, you can bring terseness and compactness in your speech and writing that will indirectly build an impressive public self-image for you in the eyes of your audience. There are a number of nouns starting with O that can help you achieve that goal.

By inserting such nouns beginning with O in the phrases, clauses and sentences you utter will bring you great success. This article will also help you in improving your English language skills and clear up any confusion you might have over the use of nouns that start with O in your writings and interactions.