O
- Obeisance – bow
- Obfuscate – confuse
- Obscure – vague, hide, not clearly understood or expressed, unknown, unnoticeablep
- Obsequy – funeral ceremony
- Obstinate – stubborn, hard to control and treat
- Occlude – shut, close
- Occult – mysterious, secret, supernatural
- Odious – hateful, vile
- Odoriferous – giving off an odor
- Odyssey – long, eventful journey
- Officious –bossy, over jealous, interfering
- Ominous – threatening, sinister, inauspicious
- Onerous – involving a great deal of effort, trouble or difficulty
- Onus – burden, responsibility
- Opportune – timely, well chosen
- Opprobrium – criticism, public disgrace from shameful conduct
- Opulence – extreme wealth, luxuriousness
- Ordeal – painful experience, trouble
- Orgy – wild party where there is excessive drinking and sexual activity
- Ostensible – stated or appearing to be true but not necessarily so, supposed, alleged
- Ostracize – ban
- Oust – expel, drive out
- Overweening – open to view
Outlandish – peculiar, unconventional
