365 Adjectives That Start with O | List with Definitions and Examples

As you may know, adjectives that start with O are not so plenty as other alphabets, like B, C, S… But still, they are equally important and indispensable in English language.

Adjectives starting with O are used to describe or modify nouns pronouns, making your writing and speaking much more specific, and a lot more interesting. Let’s take a look at some examples including adjectives beginning with O.

  • There is an open suitcase on the ground.
  • My brother and I live on opposite sides of the city.
  • It’s an obvious fact that Jim loves her.
  • This is just an ordinary book.

We can see by adding descriptive words that start with O in above sentences, the messages they convey are immediately clear and specific.

Continue reading to get a full list of adjectives that start with O, as well as definitions and examples.

Adjectives That Start with O – Full List (365 words)

  • Oafish
  • Oaken
  • Oaten
  • Obdurate
  • Obedient
  • Obese
  • Objectionable
  • Objective
  • Oblanceolate
  • Oblate
  • Obligate
  • Obligated
  • Obligational
  • Obligatory
  • Obliging
  • Oblique
  • Obliterable
  • Obliterate
  • Obliterated
  • Oblivious
  • Oblong
  • Obnoxious
  • Obovate
  • Obscene
  • Obscure
  • Obsequious
  • Observable
  • Observant
  • Observational
  • Observing
  • Obsessional
  • Obsessive
  • Obsolescent
  • Obsolete
  • Obstetric
  • Obstetrical
  • Obstinate
  • Obstreperous
  • Obstructed
  • Obstructive
  • Obtainable
  • Obtrusive
  • Obtuse
  • Obvious
  • Occasional
  • Occidental
  • Occipital
  • Occluded
  • Occlusive
  • Occult
  • Occupational
  • Occupied
  • Occurrent
  • Oceangoing
  • Oceanic
  • Ocellated
  • Ocher
  • Ochre
  • Octagonal
  • Octal
  • Octangular
  • Octogenarian
  • Octosyllabic
  • Octuple
  • Ocular
  • Odd
  • Oddish
  • Odiferous
  • Odious
  • Odoriferous
  • Odorless
  • Odorous
  • Odourless
  • Oecumenic
  • Oecumenical
  • Offbeat
  • Offenseless
  • Offensive
  • Offhand
  • Offhanded
  • Official
  • Officious
  • Offish
  • Offshore
  • Offside
  • Offstage
  • Ohmic
  • Oily
  • Old
  • Olden
  • Oldish
  • Oldline
  • Oleaceous
  • Oleaginous
  • Oleophilic
  • Oleophobic
  • Olfactive
  • Olfactory
  • Oligarchic
  • Olive
  • Olivelike
  • Olympian
  • Olympic
  • Omani
  • Ominous
  • Omissible
  • Omissive
  • Omnibus
  • Omnidirectional
  • Omnifarious
  • Omnipotent
  • Omnipresent
  • Omniscient
  • Omnivorous
  • Oncologic
  • Oncoming
  • One
  • Oneiric
  • Onerous
  • Onetime
  • Ongoing
  • Online
  • Only
  • Onomastic
  • Onshore
  • Onside
  • Onstage
  • Ontogenetic
  • Ontological
  • Onymous
  • Oozy
  • Opalescent
  • Opaline
  • Opaque
  • Open
  • Opencast
  • Opencut
  • Openhanded
  • Openhearted
  • Openmouthed
  • Operable
  • Operant
  • Operatic
  • Operating
  • Operational
  • Operative
  • Operculate
  • Operculated
  • Operose
  • Ophthalmic
  • Opinionated
  • Opinionative
  • Opponent
  • Opportune
  • Opportunistic
  • Opposed
  • Opposing
  • Opposite
  • Oppositive
  • Oppressive
  • Opprobrious
  • Optative
  • Optic
  • Optical
  • Optimal
  • Optimistic
  • Optimum
  • Optional
  • Opulent
  • Oracular
  • Oral
  • Orange
  • Orangish
  • Oratorical
  • Orbicular
  • Orbiculate
  • Orbital
  • Orbitual
  • Orchestral
  • Ordained
  • Ordered
  • Orderly
  • Ordinal
  • Ordinary
  • Organic
  • Organicistic
  • Organisational
  • Organised
  • Organismal
  • Organismic
  • Organizational
  • Organized
  • Orgiastic
  • Oriental
  • Orientated
  • Oriented
  • Original
  • Originative
  • Ornamental
  • Ornate
  • Ornery
  • Ornithological
  • Oropharyngeal
  • Orotund
  • Orphaned
  • Orphic
  • Orthodox
  • Orthogonal
  • Orthomolecular
  • Orthopaedic
  • Orthopedic
  • Orthopedical
  • Orthoptic
  • Orthostatic
  • Orthotropous
  • Orwellian
  • Oscine
  • Oscitant
  • Osseous
  • Ossicular
  • Ossiculate
  • Ossiferous
  • Ossified
  • Osteal
  • Ostensible
  • Ostensive
  • Ostentatious
  • Other
  • Otherwise
  • Otherworldly
  • Otic
  • Otiose
  • Ototoxic
  • Ottoman
  • Outback
  • Outboard
  • Outbound
  • Outbred
  • Outcast
  • Outcaste
  • Outclassed
  • Outdated
  • Outdoor
  • Outer
  • Outermost
  • Outflowing
  • Outgoing
  • Outlandish
  • Outlaw
  • Outlawed
  • Outlying
  • Outmoded
  • Outmost
  • Outraged
  • Outrageous
  • Outre
  • Outrigged
  • Outright
  • Outside
  • Outsized
  • Outspoken
  • Outspread
  • Outstanding
  • Outstretched
  • Outward
  • Oval
  • Ovarian
  • Ovate
  • Over
  • Overabundant
  • Overactive
  • Overaged
  • Overaggressive
  • Overall
  • Overambitious
  • Overanxious
  • Overarm
  • Overbearing
  • Overblown
  • Overbold
  • Overburdened
  • Overbusy
  • Overcareful
  • Overcast
  • Overcautious
  • Overconfident
  • Overcooked
  • Overcredulous
  • Overcritical
  • Overcrowded
  • Overcurious
  • Overdelicate
  • Overdressed
  • Overdue
  • Overemotional
  • Overenthusiastic
  • Overexcited
  • Overfamiliar
  • Overfed
  • Overfond
  • Overfull
  • Overgenerous
  • Overgreedy
  • Overgrown
  • Overhand
  • Overhanded
  • Overhasty
  • Overhead
  • Overheated
  • Overindulgent
  • Overjealous
  • Overjoyed
  • Overladen
  • Overland
  • Overlarge
  • Overlying
  • Overmodest
  • Overmuch
  • Overnice
  • Overnight
  • Overoptimistic
  • Overpowering
  • Overpriced
  • Overprotective
  • Overproud
  • Overqualified
  • Overrated
  • Overrefined
  • Overripe
  • Oversea
  • Overseas
  • Oversensitive
  • Overserious
  • Oversewn
  • Oversexed
  • Overshot
  • Oversize
  • Oversized
  • Oversolicitous
  • Overstrung
  • Overstuffed
  • Oversubscribed
  • Oversuspicious
  • Overt
  • Overvaliant
  • Overweening
  • Overweight
  • Overwhelmed
  • Overwhelming
  • Overworked
  • Overwrought
  • Overzealous
  • Oviform
  • Ovine
  • Oviparous
  • Ovoid
  • Ovoviviparous
  • Owing
  • Owlish
  • Own
  • Owned
  • Ownerless
  • Oxidative
  • Oxidised
  • Oxidizable

Adjectives That Start with O – with Definitions and Examples


Positive Adjectives That Start with O to Describe a Person

1. Obedient

Definition: complying or willing to comply with an order or request; submissive to another’s authority

Synonyms: compliant, tractable, amenable

Example: He was always obedient to his father’s wishes.

2. Obliging

Definition: ready to do favors; helpful; courteous; accommodating

Synonyms: helpful, accommodating, willing

Example: He found an obliging doctor who gave him the drugs he needed.

3. Observant

Definition: paying careful attention; keenly watchful; perceptive or alert

Synonyms: alert, sharp-eyed, eagle-eyed

Example: An observant shop assistant had remembered exactly what the man was wearing.

4. Omnipotent

Definition: having unlimited power or authority; all-powerful

Synonyms: supreme, almighty, dictatorial

Example: Nature is powerful, but not omnipotent: history too often influences events.

5. Omniscient

Definition: knowing everything, all-seeing

Synonyms: all-knowing, all-wise

Example: In other words, only an omniscient analyst can judge the degrees of cost and pay-off to both utterer and receiver.

6. Optimistic

Definition: having the tendency to take the most hopeful or cheerful view of matters or to expect the best outcome

Synonyms: cheerful, positive, hopeful

Example: I’m very optimistic about our chances of success.

7. Opulent

Definition: very wealthy or rich; characterized by abundance; luxuriant

Synonyms: luxurious, sumptuous, palatial

Example: Most of the cash went on supporting his opulent lifestyle.

8. Open-minded

Definition: willing to consider new ideas; unprejudiced

Synonyms: unbiased, unprejudiced, accepting

Example: Try to keep an open mind until you’ve heard all the facts.

Positive Adjectives That Start with O to Describe an Event

1. Occasional

Definition: of irregular occurrence; happening now and then; infrequent

Synonyms: intermittent, irregular, infrequent

Example: The weather was good except for an occasional shower.

2. Opaque

Definition: not letting light pass through; not transparent or translucent; not reflecting light; not shining or lustrous;

Synonyms: dull, dark, cloudy, blurred

Example: You can always use opaque glass if you need to block a street view.

3. Opportune

Definition: happening or done at the right time; seasonable; well-timed; timely

Synonyms: suspicious, propitious, favorable

Example: This would seem to be an opportune moment for reviving our development plan.

4. Original

Definition: having to do with an origin, first, earliest; fresh, new, novel; capable of or given to inventing or creating something new, or thinking or acting in an individual, fresh way; coming from someone as the originator, maker, author, etc

Synonyms: indigenous, native, first, early

Example: Never be afraid to be yourself. Remember, an original is worth more than a copy.

5. Orthodox

Definition: conforming to the usual beliefs or established doctrines, as in religion, politics, etc.; approved or conventional

Synonyms: conservative, traditional, devout

Example: We would prefer a more orthodox approach/solution to the problem.

6. Ostentatious

Definition: characterized by or given to pretentious or conspicuous show in an attempt to impress others

Synonyms: showy, conspicuous, obtrusive

Example: They criticized the ostentatious lifestyle of their leaders.

7. Obtainable

Definition: capable of being acquired

Synonyms: available, in circulation, in season

Example: Buff Fitness Center assured obtainable results for every client simply by sticking to a daily 45-minute exercise.

8. Ongoing

Definition: something that is still going on at the present time and is going to continue

Synonyms: underway, in progress, happening

Example: Training is part of our ongoing career development program.

9. Operative

Definition: functioning or having effect

Synonyms: in force, effective, valid

Example: The commercial telephone service was no longer operative.

10. Obligatory

Definition: required by a legal, moral, or other rule; compulsory

Synonyms: compulsory, mandatory, incumbent

Example: The college authorities have now made these classes obligatory.

11. Occupational

Definition: relating to a job or profession

Synonyms: professional, vocational, business

Example: For many years, experts in occupational health have puzzled over symptoms reported by office workers, including headache, nausea and fatigue.

12. One-time

Definition: Belonging to some prior time

Synonyms: sometime, erstwhile, as was

Example: The scholarship is available on a competitive basis and is a onetime award.

Positive Adjectives That Start with O to Describe a Place

1. Opulent

Definition: ostentatiously, costly and luxurious.

Synonyms: luxurious, sumptuous, lavish

Example: These were the glittering and opulent reminders of the medieval city.

2. Outstanding

Definition: prominent; distinguished; excellent; marked by superiority or distinction

Synonyms: excellent, marvelous, magnificent

Example: This is an area of outstanding natural beauty.

3. Open

Definition: someone or something which is not closed

Synonyms: unlocked, unfolded, unlatched

Example: He could see a green open space just beyond; and then the woods seemed to be thicker and darker.

4. Ornamental

Definition: serving or intended as an ornament; decorative.

Synonyms: fancy, attractive, artistic

Example: The stream was dammed up to form ornamental lakes.

5. Ornate

Definition: elaborately or highly decorated

Synonyms: decorated, embellished, adorned

Example: The church has an ornate black and white marbled interior.

6. Oaken

Definition: Consisting of or made of wood of the oak tree

Synonyms: oak tree, oak wart, woody

Example: A new oaken enclosure was built and new wiring and electric bellows bought.

7. Odorless

Definition: having no odor, fragrance-free

Synonyms: unscented, deodorized, un-perfumed

Example: the chemical compound is not toxic as such and it is odorless.

8. Official

Definition: Given official status as a national or state institution

Synonyms: formal, ceremonial, pompous

Example: The mayor presented him with a gold medal at an official city reception.

9. Offshore

Definition: At some distance from the shore

Synonyms: away from the shore line, shoreward

Example: His money is in an offshore island bank.

Positive Adjectives That Start with O to Describe Emotions, Personality, and Feelings

1. Objectionable

Definition: disagreeable; offensive

Synonyms: distasteful, unpleasant, displeasing

Example: His drunken behavior was extremely objectionable.

2. Overjoyed

Definition: extremely happy

Synonyms: ecstatic, euphoric, delighted

Example: He was overjoyed to see his mother again.

3. Obliging

Definition: Showing a cheerful willingness to do favors for others

Synonyms: helpful, accommodating, willing

Example: He is an extremely pleasant and obliging man.

4. Obvious

Definition: easily perceived or understood; clear, self-evident, or apparent

Synonyms: evident, clear, conspicuous

Example: Lack of qualifications is an obvious disadvantage.

Negative Adjectives That Start with O to Describe a Person

1. Odd

Definition: different to what is usual or expected; strange

Synonyms: strange, peculiar, weird

Example: As a manager, it is so hard to deal with odd workers.

2. Obese

Definition: very fat; stout; corpulent

Synonyms: overweight, gross, stout

Example: Obese people tend to have higher blood pressure than lean people.

3. Obtuse

Definition: slow to understand or perceive; dull or insensitive

Synonyms: stupid, dull, unintelligent

Example: He wondered if the doctor was being deliberately obtuse.

4. Offensive

Definition: unpleasant, as to the senses; disgusting; repugnant; causing resentment, anger, etc

Synonyms: insulting, rude, derogatory

Example: His comments were deeply offensive to a large number of single mothers.

5. Oafish

Definition: Ill-mannered and coarse, contemptible in behavior or appearance

Synonyms: stupid, foolish, idiotic

Example: My fellow, oafish roommate has shared my computer with me periodically.

6. Oblivious

Definition: not aware of or concerned about what is happening around one

Synonyms: unaware, heedless, insensible

Example: He seemed oblivious to the fact that he had hurt her.

7. Obstinate

Definition: Resistant to guidance or discipline

Synonyms: stubborn, unyielding, inflexible

Example: The most obstinate farmers were persecuted and imprisoned.

8. Obstructive

Definition: causing or tending to cause deliberate difficulties and delays

Synonyms: uncooperative, awkward, disobliging

Example: Mr Smith was obstructive and refused to follow correct procedure.

9. Old

Definition: having lived for a long time; no longer young

Synonyms: elderly, mature, aged

Example: There is no better looking-glass than an old friend

10. Oversized

Definition: bigger than the usual size

Synonyms: bulging, floppy, droopy

Example: Fashion gurus dictate crazy ideas such as squeezing oversized bodies into tight trousers.

11. Oily

Definition: containing oil

Synonyms: greasy, fatty, buttery

Example: When she was younger, she had very oily skin.

Negative Adjectives That Start with O to Describe an Event

1. Obscure

Definition: not discovered or known about; uncertain

Synonyms: uncertain, doubtful, unclear

Example: The origins of the tradition have become obscure.

2. Obsolete

Definition: no longer in use or practice; discarded

Synonyms: outdated, old-fashioned, outmoded

Example: Electronic banking may make over the counter transactions obsolete.

3.  Opposing

Definition: set against; placed opposite, in balance or contrast; contending with in speech or action

Synonyms: rival, opposite, combatant

Example: The soldiers battled against the opposing army all day.

4. Obscene

Definition: offensive to morality or decency; indecent; depraved

Synonyms: indecent, salacious, smutty, pornographic

Example: In the raid, police found several boxes of obscene videotapes.

5. Opposite

Definition: different in every way; exactly contrary

Synonyms: conflicting, incompatible, contrasting

Example: They hit a truck coming in the opposite direction.

6. Offline

Definition: not controlled by or directly connected to a computer or the internet.

Synonyms: disconnected, logged off, connectionless

Example: If one or more modules are offline, you will need to repeat this call when all modules are available online.

Negative Adjectives That Start with O to Describe a Place

1. Odorous

Definition: having or giving off an odor

Synonyms: smelly, stinking, reeking

Example: This can in fact be quite useful in some circumstances such as where a person works in an odorous environment.

2. obdurate

Definition: Showing unfeeling resistance to tender feelings

Synonyms: stubborn, obstinate, intransigent

Example: Actually, there are some fairly obdurate myths about the London climate.

3. Occupied

Definition: (of a building, seat, etc.) being used by someone

Synonyms: inhabited, tenanted, live in

Example: Only the ground floor is fully occupied.

4. Odoriferous

Definition: having or giving off a smell, especially an unpleasant one

Synonyms: aromatic, pungent, savory

Example: These odoriferous organic compounds contain numerous ingredients generally classified into four main groups which are characteristic of the majority of essential oils.

Negative Adjectives That Start with O to Describe Emotions, Personality, and Feelings

1. Ominous

Definition: giving the worrying impression that something bad is going to happen; threateningly inauspicious

Synonyms: menacing, baleful, sinister

Example: There was an ominous silence at the other end of the phone.


Definition: having the nature of, involving, or doing great injury or wrong; exceeding all bounds of decency or reasonableness; very offensive or shocking; unrestrained

Synonyms: shocking, disgraceful, appalling

Example: I must make apologies for my outrageous behavior.

3. Obnoxious

Definition: extremely unpleasant, causing disapproval

Synonyms: nasty, distasteful, disagreeable

Example: I have been in restaurants where the human customers have been loud, rude and obnoxious.

4. Oppressive

Definition: inflicting harsh and authoritarian treatment

Synonyms: harsh, cruel, brutal

Example: The oppressive afternoon heat had quite tired him out.

Final Thoughts on Adjectives That Start with O

Do you like these adjectives that start with the letter O we sorted out for you? We hope you find them helpful.

Generally, nouns are one of the most important parts of speech. But adjectives make your speech more accurate and understandable. The thing with adjectives is you never want to overdo them.

Too many adjectives can bulk up a sentence, reducing its fluidity. So remember, only to use these adjectives that start with O where appropriate.

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