| overzijde | other side |
| Ovezgeldy Atajev | Öwezgeldi Ataýew |
| Ovide Decroly | Ovide Decroly |
| Ovide en zijn vriendjes | Ovide and the Gang |
| Ovidijus Vyšniauskas | Ovidijus Vyšniauskas |
| Ovidius | Ovid |
| Oviedo | Oviedo |
| ovipaar | oviparous |
| Oviraptor | Oviraptor |
| Oviraptorosauria | Oviraptorosauria |
| ovulatie | ovulation |
| ovuleren | ovulate |
| ovulum | ovule |
| ovum | ovum |
| Owadja Sforno | Obadiah ben Jacob Sforno |
| Owain Glyndwr | Owain Glyndŵr |
| Owambo | Ovambo |
| Owamboland | Ovamboland |
| Owen Seymour Arthur | Owen Arthur |
| Owen Stanley-gebergte | Owen Stanley Range |
| Owen Willans Richardson | Owen Willans Richardson |
| Owen Wilson | Owen Wilson |
| Owens Valley | Owens Valley |
| Owingen | Owingen |
| Oxalidales | Oxalidales |
| Oxalylchloride | Oxalyl chloride |
| Oxelösund | Oxelösund Municipality |
| Oxfam International | Oxfam |
| Oxford | Oxford |
| Oxford Circus | Oxford Circus tube station |
| Oxford Classical Dictionary | Oxford Classical Dictionary |
| Oxford English Dictionary | Oxford English Dictionary |
| Oxford Street | Oxford Street |
| Oxfordien | Oxonian |
| Oxfordshire | Oxfordshire |
| Oxidatietoestand | Oxidation state |
| Oxidatieve fosforylering | Electron transport chain |
| Oxidator | Oxydizing |
| Oxide | Oxide |
| oxo | tick-tack-toe |
| Oxonium | Hydronium |
| Oxycodon | Oxycodone |
| oxydatie | oxidation |
| oxyde | oxide |
| oxyderen | oxygenate |
| Oxyliquiet | Oxyliquit |
| Oxymetazoline | Oxymetazoline |
| Oxymoron | Oxymoron |
| Oxyrrhynchus | Oxyrhynchus |
| Oxytocine | Oxytocin |
| Oy-Mittelberg | Oy-Mittelberg |
| Oyo | Oyo State |
| Oyten | Oyten |
| Oyón-Oion | Oyón-Oion |
| Oz | Ounce |
| Oza dos Ríos | Oza dos Ríos |
| Ozama | Ozama River |
| Ozamis City | Ozamiz City |
| Ozimek | Ozimek |
| ozon | ozone |
| Ozongat | Ozone layer |
| Ozonwater | Hydrogen peroxide |
| Ozorków | Ozorków |
| Ozzy Osbourne | Ozzy Osbourne |
| Oßmannstedt | Oßmannstedt |
| Oñati | Oñati |
| Oöliet | Roestone |
| Oława | Oława |
| Ośno Lubuskie | Ośno Lubuskie |
| Oţelul Galaţi | Oţelul Galaţi |
| Ożarów | Ożarów |
