Oblivious (Adjective) - भुलक्कड़
Synonyms:Careless, Forgetful, Ignorant, Negligent.

Obnoxious (Adjective) - घृणित/अप्रिय
Synonyms:Abhorent, Abominable, Odious, Repulsive.

Obvious (Adjective) - स्पष्ट/प्रत्यक्ष
Synonyms:Apparent, Clear, Transparent, Distinct.

On Looker (Noun) - दर्शक
Synonyms:Observer, Spectator, Watcher, Witness, Viewer.

Opaque (Adjective) - अपारदर्शक
Synonyms:Cloudy, Obscure, Unclear, Dim.

Opponent (Noun) - शत्रु/विरोधी
Synonyms:Challenger, Antagonist, Enemy, Foe.

Orator (Noun) - वक्ता
Synonyms:Lecturer, Preacher, Speaker.

Optional (Adjective) - वैकल्पिक/ऐच्छिक
Synonyms:Extra, Voluntary, Possible.

Overcome (Verb) - जितना/विजय प्राप्त करना
Synonyms:Defeat, Over Throw, Triumpth.

Owner (Noun) - स्वामी/अधिकारी
Synonyms:Lord, Master, Proprietor.