| oast | n. | drying kiln, esp. for hops | ||
| obambulate | v. | to walk around, to wander | ||
| obduracy | n. | stubborn inflexibility, state of being unmoved or unashamed | ||
| obiter dictum | n. | judicial opinion incidental to a given case, and thus not legally binding | Latin | |
| objective tinnitus | n. | noise heard within the ear which can also be heard by another (usu. through an instrument such as a stethoscope) | ||
| objurgate | v. | to chide or scold or rebuke | ||
| oblate | adj. | flattened at the poles | ||
| oblation | n. | office or sacrament of the Eucharist; religious or charitable offering | ||
| obliquity | n. | state or condition of being neither parallel nor perpendicular, quality of being oblique; mental perverseness | ||
| obliviscence | n. | forgetfulness, an act of forgetting | ||
| oblong | adj. | neither square nor circular, having length in one dimension greater than in another; elongated | ||
| obnoxious | adj. | exposed to danger | archaic | |
| obnubilation | n. | overclouding, darkening as with clouds; esp. clouding of mental facilities | ||
| obreption | n. | acquirement of a thing through fraud; (law) obtaining (a gift, a dispensation, etc.) by false statement | ||
| obsequy | n. | funeral rite | ||
| obstreperous | adj. | unruly; characterized by great noise or outcry | ||
| obstupefy | v. | to stupefy, esp. mentally | ||
| obtrude | v. | to thrust forward unduly; to push (something) upon a person, esp. without invitation | ||
| obtrusive | adj. | projecting or imposing in the way; overly forward | ||
| obtund | v. | to dull, to blunt | ||
| obus | n. | artillery shell | ||
| ochlocracy | n. | mob-rule | ||
| odium | n. | intense hatred or disgust; opprobrium, reproach | ||
| ods bodikins | int. | interjection palliating stronger phrase “God’s bodkins” (meaning the nails used to affix Jesus to the cross) | archaic | |
| oeillade | n. | amorous look or stare | ||
| of even date | adj. | of the same date | law | |
| ofay | n. | white person | slang | |
| office | n. | tip-off, warning | slang | |
| ogdoad | n. | group of eight, octet | ||
| ogee | n. | double curve with S-shaped cross-section | architecture | |
| ogive | n. | [statistics] graph of cumulative distribution function; [architecture] roundly pointed arch, rib supporting such an arch | ||
| oho | int. | exclamation of surprise, elation, recognition | ||
| oik | n. | oaf; lower class person | slang | |
| okta | n. | measurement of cloud cover equal to one eighth of the entire sky | ||
| oleograph | n. | picture printed in oil colors on cloth or canvas in imitation of an oil painting | ||
| oliguria | n. | scanty production of urine | ||
| omadhaun | n. | foolish male | ||
| omentum | n. | fold of peritoneum connecting stomach with spleen, liver, colon; caul | biology | |
| omnibus | n. | bus | archaic | |
| omnigenous | adj. | of all kinds | ||
| on foot of | adv. | because of | idiom | |
| on one’s uppers | adj. | very poor, destitute [from idea of poverty so acute that one’s shoes have worn away all the leather, so that only the upper portion remains] | British | |
| on the fiddle | adj. | of someone engaged in petty cheating | slang | |
| on the lash | adj. | drinking socially, usu. to excess | British | |
| on the tapis | adj. | under consideration, up for discussion | idiom | |
| onager | n. | Asiatic wild ass; ancient rock-hurling siege weapon | ||
| one-arm joint | n. | restaurant in urban centers with only single chairs with small table surface for diners’ use | slang | |
| oneiric | adj. | of or related to dreams or dreaming | ||
| oneirophrenia | n. | hallucinatory state of dreamlike perception, often caused by severe sleep deprivation | ||
| onomastic | adj. | of or related to personal or geographical names |
