90 Adjectives That Start With “O”

Few things in life offer such perfection as the letter “O.” It’s a perfect circle, an outstanding shape that forms some of the most optimal adjectives you’ll ever see. Adjectives are that special ingredient that help nouns become more opulent, ostentatious, or just plain ordinary. Adjectives that start with “O” give you an overflowing amount of options for your everyday vocabulary.

list of four adjectives that start with "O" list of four adjectives that start with "O"
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Positive Adjectives That Start With “O”

“O” adjectives offer a whole spectrum of positivity for you to play with. Are you having an okay time or an outstanding time? With the right positive adjective, your jewelry can be ornate or opalescent, and you can be more optimistic and outgoing.

Adjective Definition Synonyms
obliging ready to do favors; helpful; courteous; accommodating friendly, amiable, hospitable
observant quick to notice or perceive alert, watchful, careful
odds-on having a strong chance of succeeding or winning favorite, predictable, likely
okay (or OK) correct; meeting standards; proceeding normally satisfactory, acceptable
omnicompetent able to deal with all matters or situations multitalented, capable, efficient
one-of-a-kind unique original, distinct, rare
opalescent displaying a variety of colors, like an opal iridescent, prismatic, multi-colored
open-hearted not reserved; kindly or benevolent compassionate, friendly, generous
open-minded unbiased; consider new ideas receptive, approachable, understanding
opportune happening or done at the right time; seasonable; well-timed; timely advantageous, auspicious, felicitous
optimal best; most favorable excellent, greatest, matchless
optimistic having the tendency to take the most hopeful or cheerful view of matters or to expect the best outcome positive, hopeful, idealistic
optimum best; most favorable ideal, greatest, superlative
opulent very wealthy or rich; characterized by abundance extravagant, luxurious, lavish
orderly organized in a neat, tidy manner systematic, clean, well-kept
originative having the power to produce or create something creative, gifted, innovative
ornate elaborate; embellished baroque, elegant, lavish
orotund (of voice or speech) strong, full, rich, and clear bombastic, resonant, sonorous
outgoing friendly, sociable extroverted, warm, gregarious
out-of-this-world superb, extraordinary marvelous, heavenly, wonderful
outstanding prominent; distinguished; excellent; marked by superiority or distinction exceptional, impressive, magnificent
overjoyed extremely happy; delighted joyful, euphoric, jubilant

Negative Adjectives That Start With “O”

Unfortunately, not all moments call for positivity. Sometimes, you need a negative adjective starting with “O” to describe any objectionable offenses, obscene occasions, or odious occurrences.

Adjective Definition Synonyms
objectionable disagreeable; offensive unpleasant, deplorable, repulsive
oblique slanting; indirectly stated or expressed; evasive backhanded, vague, sideways
obliterated destroyed utterly eliminated, annihilated, erased
oblivious not aware of or concerned; unmindful; forgetful unconscious, unaware, ignorant
obnoxious very unpleasant offensive, detestable, hateful
obscene offensive to one's feelings, or to prevailing notions of modesty or decency; lewd indecent, bawdy, crude
obscure not clear; uncertain confusing, enigmatic, ambiguous
obstinate stubbornly adhering to one’s opinion inflexible, dogmatic, headstrong
obstructive blocking, hindering, or interrupting; deliberately causing delays unhelpful, difficult, unaccommodating
obtrusive noticeable in an intrusive or unwelcome way obvious, meddlesome, intrusive
obtuse slow to understand or perceive; dull or insensitive blunt, dense, imperceptive
odious repulsive; revolting horrible, loathsome, vile
offensive unpleasant to the senses; disgusting repugnant, irritating, objectonable
officious aggressive in offering unwanted services or help; asserting authority in a domineering way bossy, meddlesome, pushy
ominous portending harm or evil foreboding, inauspicious, menacing
onerous involving a great amount of effort that can feel oppressively burdensome arduous, exhausting, laborious
opinionated stubborn or conceited in regard to the merits of one’s opinions dogmatic, cocky, bullheaded
opportunistic taking advantage of the situation for personal benefit conniving, wily, devious
oppressive unjust treatment; cruel; tyrannical overwhelming, burdensome, inhuman
ostentatious characterized by or given to pretentious or conspicuous show in an attempt to impress others gaudy, highfalutin, egotistic
overbearing overpowering or domineering bossy, imperious, oppressive
overblown overinflated; excessive pretentious, disproportionate, turgid
overloaded loaded with an excessive burden overworked, strained, stressed
oversimplified simplified to the point of misrepresenting facts simplistic, unnuanced, distorted
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Neutral Adjectives That Start With “O”

Of course, most of life isn’t just positive or negative. Most people, places, and objects just exist, but that doesn’t mean they should go without some good descriptors. From odd cookies to omnivorous bears, “O” adjectives offer plenty of optional ornaments for your nouns.

Adjective Definition Synonyms
obese fat; stout corpulent, plump, portly
obsolete no longer in use or practice; discarded antiquated, dated, archaic
obvious clear; apparent understandable, overt, noticeable
occasional of irregular occurrence; happening now and then sporadic, intermittent, infrequent
odd not usual or ordinary; singular; peculiar; strange different, unusual, bizarre
offbeat unusual strange, unconventional, idiosyncratic
oily of, like, consisting of, or containing oil; smooth or unctuous in character or manner slippery, buttery, slick
older not young; lived for a long time elder, senior
old-fashioned behind the times; not current antiquated, dated, outmoded
omnipotent having unlimited power or authority; all-powerful almighty, godlike, unrestricted
omniscient having infinite knowledge; knowing all things all-know, all-seeing, pansophical
omnivorous eating both plants and animals; taking in everything predatory, ravenous, gluttonous
opaque not letting light pass through; not transparent or translucent cloudy, hazy, murky
operable usable; can be used feasible, doable, practicable
operative functioning; effective active, usable, functional
opposing/opposed set against; placed opposite, in balance or contrast; contending within speech or action resisting, antagonistic, conflicting
opposable (of thumbs) capable of touching other digits on hand prehensile
opposite different in every way; exactly contrary antithetical, unlike, contradictory
optional not required; left to your own choice noncompulsory, nonobligatory, discretional
oral spoken by the mouth vocal, articulate, phonated
orange color between red and yellow red-yellow, carrot
ordinary not special; normal; usual everyday, typical, common
original having to do with an origin; fresh, new, novel initial, creative, earliest
ornamental decorative showy, dressy, embellishing
orthodox conforming to the usual beliefs or established doctrines, as in religion, politics, etc. traditional, conventional, conservative
outlandish bizarre; unfamiliar; weird strange, eccentric, peculiar
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“O” Adjectives To Describe a Person

Plenty of the adjectives above offer some excellent, obvious descriptors for people, but it doesn’t hurt to arm yourself with plenty of official “O” adjectives to describe a person.

Adjective Definition Synonyms
oafish clumsy; uncultured blundering, bumbling, graceless
obedient obeying or willing to obey; submissive well-behaved, compliant, faithful
obeisant showing respect deferential, reverent, dutiful
obsessive consuming; being consumed compulsive, controlling, fanatical
occupied active or busy engrossed, engaged, employed
ornery stubborn; unpleasant in disposition or temper cranky, grumpy, ill-tempered
outcast rejected or discarded; cast out unwanted, unaccepted, undesirable
outdoorsy extremely fond of outdoor life nature-loving
outrageous having the nature of, involving, or doing great injury or wrong; very offensive or shocking disgraceful, scandalous, startling
outspoken express opinions directly; blunt candid, forthright, frank
overachieving performing better or accomplishing more than expected outperforming, intellectual, phenomenal
overbold excessively bold blatant, conspicuous, shameless
overconfident extremely confident brash, careless, cocky
overcritical extremely critical hypercritical, nit-picking, disparaging
overextended exhausted; stressed out fatigued, overworked, burdened
overprotective excessively protective vigilant, shielding, restrictive
overqualified having more experience, training, or education than required for a job or position worldly, scholarly, well-read
overwrought extremely excited or agitated frantic, emotional, worked-up
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Example Sentences for Adjectives That Start With “O”

Knowing all these adjectives that start with “O” is just half the battle. You have to learn how to actually use them until you feel overconfident and overqualified.

  1. My open-minded friend was willing to try just about anything at least once.
  2. I had the onerous task of alphabetizing all of our spices and condiments.
  3. She made a one-of-a-kind mug in her ceramics class.
  4. Despite his offbeat personality, he was extremely relatable and easy to get along with.
  5. He was ashamed of the glass cup that had gotten increasingly opaque from sitting on his desk for so long.
  6. After weeks of being under construction, the elevator was finally operable.
  7. The obnoxious combination of screaming kids and someone practicing the bagpipes made it hard for him to get any rest.
  8. He was worried about the ominous work email that simply read, “Do you have time to talk?”
  9. Aside from the occasional pepperoni pizza, his diet was mostly vegetarian.
  10. The oppressive heat made it hard for her to want to do anything other than read in an air-conditioned cafe.
  11. The French fries were oily, but that’s exactly how he liked them.
  12. Our outgoing friend was always talking to strangers and making friends with store workers.
  13. This seemed like an opportune moment to remind the kids not to push and shove each other when the bell rang.
  14. The final exam involved a written test and an oral presentation.
  15. Whenever he felt himself losing hope, he talked to his optimistic friend.
  16. She appreciated the fine artistry and ornate details in the statue.
  17. The camp ranger taught us about the omnivorous bears that loved to eat meat, roots, and marshmallows.
  18. The overjoyed team learned they had two days off this week.
  19. The whole class did such an outstanding job on the test that she told them they’d have pizza and ice cream to celebrate.
  20. They spent two hours discussing the optimum amount of salsa for tortilla chips.
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Oh! Even More “O” Words

With your brain overloaded with adjectives starting with “O,” you can expand your vocabulary further with other parts of speech. Learning more words that start with “O” will improve your writing and conversational abilities, and it just might help you get the winning score in your word games.