0 Most important 500 Word List for TOEFL Test (O)

OBDURATE: Hard-hearted; stubborn - an obdurate, unrepentant criminal. Synonyms: adamant, unyielding, inflexible. Antonyms: submissive, docile, compliant.

OBLIVIOUS (noun: OBLIVION): Forgetful; absent-minded - walking oblivious of his surroundings. Synonyms: unmindful, heedless, abstracted.

OBSESSION: A persistent feeling, idea, activity, etc., which dominates a person; the state of being exclusively preoccupied by a fixed idea - Now that he has learned bowling, it has become his obsession. Synonyms: mania, infatuation (a foolish passion), monomania.

OBSOLETE: No longer in use - an obsolete word, not even included by most dictionaries. Synonyms: archaic, antiquated.

OBTRUSIVE (verb: OBTRUDE): Thrusting oneself or itself into undue prominence - made himself obnoxiously obtrusive. Synonyms: intrusive, aggressive.

OBVIATE: To prevent, dispose of, or make unnecessary by appropriate actions - an act which obviated all objections. Synonyms: preclude, forestall.

OMNIPOTENT: All-powerful - an omnipotent despot.

ONUS: Burden; duty; obligation - bore the onus of his difficult office creditably.

OSTENSIBLE: Apparent; pretended - his ostensible, though not actual, purpose. Synonyms: professed, plausible (that is, appearing true, reasonable, or fair), specious.

OSTRACIZE: To banish; to exclude from public favor or privileges - a former premier ostracized by popular vote. Synonym: outlaw.