| pacific | Peaceful in character or intent | |
| overweening | Showing excessive confidence or pride | |
| outmoded | Old-fashioned or outdated | |
| ostracized | To exclude someone from a society or group | |
| ostentatious | Characterized by vulgar or pretentious display; designed to impress or attract notice | |
| ossified | Turned into bone; become bony | |
| orthodox | Adhering to the accepted or traditional and established faith, especially in religion | |
| opulent | ostentatiously rich and luxurious or lavish | |
| opportune | Well-chosen or particularly favorable or appropriate | |
| opine | To express an opinion | |