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GRE words starting with O

98 GRE-level words that begin with O, each with its part of speech, a plain-English definition, and an example sentence. Tap any word for synonyms, antonyms, and more.

oafnoun

a stupid, clumsy, or boorish person

obdurateadjective

stubbornly refusing to change one's mind or course of action

obeisancenoun

a gesture or attitude of deep respect or submission

obeisantadjective

showing deferential respect or submissive obedience

obelisknoun

a tapering stone pillar with a pyramidal top, typically erected as a monument

obeseadjective

grossly overweight to a degree that poses a health risk

obfuscateverb

to make something deliberately unclear or confusing

obfuscationnoun

the act of making something deliberately unclear or confusing

obfuscatoryadjective

tending to make something deliberately obscure, confusing, or unclear

objurgateverb

to scold or rebuke someone sharply

objurgationnoun

a harsh rebuke or severe scolding

objurgatoryadjective

expressing harsh rebuke or scolding

oblationnoun

a thing offered or presented to a deity or for a religious purpose

obligatoryadjective

required by rule, law, or custom

obliqueadjective

not expressed or done directly; slanting or evasive

obliquitynoun

the quality of being indirect, devious, or evasive; a divergence from moral rectitude

obliterateverb

to destroy or wipe out completely

oblivionnoun

the state of being completely forgotten or of being unconscious of one's surroundings

obliviousadjective

completely unaware of what is happening around one

obloquynoun

strong public criticism or verbal abuse, and the disgrace it brings

obnoxiousadjective

extremely unpleasant or objectionable in behavior or character

obnubilateverb

to darken, dim, or obscure as if with a cloud

obscurantismnoun

the deliberate prevention of clarity or opposition to enlightenment

obscureadjective

not clearly understood, or little known

obsequiousadjective

excessively eager to please or obey, in a fawning way

obsessionnoun

an idea or thought that continually preoccupies or intrudes on a person's mind

obsidiannoun

a hard, dark, glass-like volcanic rock formed by the rapid solidification of lava

obsolescentadjective

becoming obsolete, gradually passing out of use

obsoleteadjective

no longer in use or out of date

obstinateadjective

stubbornly unwilling to change opinion or behavior

obstreperousadjective

noisy and difficult to control

obtrudeverb

to impose oneself or one's ideas on others without invitation

obtrusiveadjective

noticeable in an unwelcome, intrusive way

obtundverb

to blunt or dull the force, sharpness, or sensitivity of something

obtuseadjective

slow to understand or perceive; lacking sharpness of mind

obviateverb

to prevent or make unnecessary by anticipating in advance

occludeverb

to block, close up, or obstruct a passage or opening

occultadjective

hidden from ordinary understanding or relating to the supernatural

oculistnoun

a physician who specializes in diseases and care of the eyes

odiousadjective

extremely unpleasant and deserving of hatred

odiumnoun

widespread hatred or disgust directed at someone

odoriferousadjective

having or giving off a strong, often unpleasant smell

offalnoun

the waste parts or organs of a butchered animal, or refuse and rubbish generally

offhandadjective

done or said casually, without prior thought or preparation

officiousadjective

asserting authority or offering help in an annoying, intrusive way

olfactoryadjective

relating to the sense of smell

oligarchynoun

a form of government in which power rests with a small elite group

ominousadjective

suggesting that something bad is about to happen

omnipotentadjective

having unlimited or very great power

omnipresentadjective

present everywhere at the same time

omniscientadjective

having unlimited or complete knowledge of everything

omnivorousadjective

eating both plants and animals, or consuming everything available with great eagerness

onerousadjective

involving a heavy, burdensome amount of effort or difficulty

onomatopoeianoun

the formation of a word that phonetically imitates the sound it describes

onslaughtnoun

a fierce or destructive attack or surge of something overwhelming

opalescentadjective

showing shifting changes in color like those of an opal

opaqueadjective

hard to understand, or not allowing light to pass through

opiatenoun

something that numbs the senses, dulls awareness, or causes passive acceptance

opineverb

to state one's opinion

opportuneadjective

well suited to a particular moment; timely

opprobriousadjective

expressing scornful reproach or carrying great disgrace

opprobriumnoun

harsh public condemnation and the disgrace that follows wrongdoing

optimaladjective

best or most favorable under a given set of circumstances

opulencenoun

great wealth and luxuriousness displayed in a lavish manner

opulentadjective

displaying great wealth and luxury

opusnoun

an artistic or literary work, especially one regarded as major

oracularadjective

obscurely portentous, as if delivering ambiguous prophecies

orationnoun

a formal, often elaborate, public speech

oratorionoun

a large-scale musical composition for orchestra and voices on a sacred or serious theme, performed without costumes or staging

oratorynoun

the art of formal, eloquent public speaking

ordainverb

to order or decree something officially or by authority

ordinancenoun

an authoritative order or law issued by a government, especially a local municipality

orientationnoun

the process of becoming familiar with a new situation, or the determination of one's position relative to surroundings

orificenoun

an opening, especially one in the body such as a nostril or mouth

ornateadjective

elaborately or heavily decorated

ornithologynoun

the scientific study of birds

orotundadjective

having a full, rich, pompous quality in voice or style; overly grand in manner

orthodoxadjective

conforming to established or traditional beliefs and practices

orthographynoun

the conventional spelling system of a language and the rules that govern it

oscillateverb

to move or swing back and forth, or to waver between options

oscitancynoun

drowsy inattentiveness, often expressed through yawning

oscitantadjective

drowsily inattentive and prone to yawning

ossifiedadjective

turned into bone or bony tissue, or made rigid and unable to change through habit or convention

ossifyverb

to become rigid or fixed in habit and resistant to change

ostensibleadjective

appearing to be true on the surface but possibly not genuine

ostentatiousadjective

marked by a showy display intended to impress others

ostracismnoun

exclusion from a group or society by general consent as a form of punishment

ostracizeverb

to exclude someone from a group or society

otioseadjective

serving no useful purpose; pointless or superfluous

outlandishadjective

strange, bizarre, or unconventional to the point of seeming absurd

outmodedadjective

no longer fashionable or useful; out of date

outstripverb

to surpass or exceed someone or something in growth, achievement, or performance

ovationnoun

an enthusiastic and prolonged display of public approval

overshadowverb

to make someone or something seem less important or significant by comparison

overtadjective

done or shown openly, not hidden

overturenoun

an opening move or proposal intended to start something

overweeningadjective

showing excessive confidence, pride, or presumption

overwroughtadjective

extremely agitated, or excessively elaborate in style

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