- Occident: N. the West
- obsolete: ADJ. outmoded
- obstetrician: N. physician specializing in delivery of babies
- obstinate: ADJ. stubborn; hard to control or treat
- obstreperous: ADJ. boisterous; noisy
- obtrude: V. push (oneself or one's ideas) forward or intrude; butt in; stick out or extrude
- obtuse: ADJ. blunt; stupid
- obviate: *V. make unnecessary; get rid of
- occlude: *V. shut; close
- occult: ADJ. mysterious; secret; supernatural
- oculist: N. physician who specializes in treatment of the eyes
- odious: ADJ. hateful; vile
- odium: N. detestation; hatefulness; disrepute
- odoriferous: ADJ. giving off an odor
- odorous: ADJ. having an odor
- odyssey: N. long, eventful journey
- offhand: ADJ. casual; done without prior tought
- officious: *ADJ. meddlesome; excessively pushy in offering one's services
- ogle: V. look at amorously; make eyes at
- olfactory: ADJ. concerning the sense of smell
- oligarchy: N. government by a privileged few
- omnipotent: ADJ. all-powerful
- omnipresent: ADJ. universally present; ubiquitous
- omniscient: ADJ. all-knowing
- onerous: *ADJ. burdensome
- onslaught: N. vicious assault
- onus: N. burden; responsibility
- opalescent: ADJ. iridescent; lustrous
- opaque: ADJ. dark; not transparent
- opiate: N. medicine to induce sleep or deaden pain; something that relieves emotions or causes inaction
- opportune: ADJ. timely; well-chosen
- opportunist: N. individual who sacrifices principles for expediency by taking advantage of circumstances
- opprobrium: N. infamy; vilification
- optician: N. maker and seller of eyeglasses
- optometrist: N. one who fits glasses to remedy visual defects
- opulence: N. extreme wealth; luxuriousness; abundance
- opus: N. work
- oracular: ADJ. prophetic; uttered as if with divine authority; mysterious or ambiguous
- orator: N. public speaker
- oratorio: N. dramatic poem set to music
- ordain: V. decree or command; grant holy orders; predestine
- ordeal: N. severe trial or affliction
- ordinance: N. decree
- ordination: N. ceremony conferring holy orders
- orgy: N. wild, drunken revelry; unrestrained indulgence
- orient: V. get one's bearings; adjust
- orientation: N. act of finding oneself in society
- orifice: N. mouthlike opening; small opening
- ornate: ADJ. excessively or elaborately decorated
- ornithologist: N. scientific student of birds
- orthodox: ADJ. traditional; conservative in belief
- orthography: N. correct spelling
- oscillate: *V. vibrate pendulumlike; waver
- osseous: ADJ. made of bone; bony
- ossify: V. change or harden into bone
- ostensible: ADJ. apparent; professed; pretended
- ostentatious: *ADJ. showy; pretentious; trying to attract attention
- ostracize: V. exclude from public favor; ban
- oust: V. expel; drive out
- outlandish: ADJ. bizarre; peculiar; unconventional
- outmoded: ADJ. no longer stylish; old-fashioned
- outskirts: N. fringes; outer borders
- outspoken: ADJ. candid; blunt
- outstrip: V. surpass; outdo
- outwit: V. outsmart; trick
- ovation: N. enthusiastic applause
- overbearing: ADJ. bossy; arrogant; decisively important
- overt: ADJ. open to view
- overweening: ADJ. presumptuous; arrogant