| Term | Definition |
| obstinate | stubborn; refusing to be persuaded |
| obtuse | dull; blunt; unintelligent; lacking sharpness |
| obviate | eliminate the need for something; make unnecessary |
| ominous | a sign of something inauspicious that's about to happen; inauspicious |
| onerous | burdensome; oppressive |
| opaque | too dark or thick for light to pass through |
| opportunist | someone who takes advantage of the situation |
| optimist | someone who always believes things will turn out okay |
| opulence | luxury; wealth; riches |
| pacifist | person who refuses to fight |
| paltry | worthless; insignificant, petty |
| parity | equality or equivalence; balance among a group of rivals |
| parsimony | stinginess; excessive frugality |
| partisan | blindly devoted to a cause or oraganization |
| paucity | too few; scarcity |
| pecuniary | having to do with money; financial |
| penchant | a strong liking; attraction |
| penury | extreme poverty; destituion |