| Oliwia | Olivia |
| Oliwin | Olivina |
| Oliwiny | Olivina |
| Oliwić | Olio |
| oliwka | oliva |
| Oliwka europejska | Olea europaea |
| Oliwkowate | Oleaceae |
| Oliwny | Olea europaea |
| Olkusz | Olkusz |
| Ollastra | Ollastra |
| Olli Rehn | Olli Rehn |
| Ollie | Ollie |
| Ollon | Ollon |
| Olmeta-di-Capocorso | Olmeta di Capocorso |
| Olmeta-di-Tuda | Olmeta di Tuda |
| Olmi-Cappella | Olmi Cappella |
| Olof Rudbeck starszy | Olaus Rudbeck |
| Olof Vilhelm Arrhenius | Olof Vilhelm Arrhenius |
| Olog-hai | Troll |
| Olokmińsk | Olëkminsk |
| Olongapo | Olongapo |
| Olsen Brothers | Olsen Brothers |
| olsza | ontano |
| Olsza szara | Alnus incana |
| Olsztyn | Olsztyn |
| Oltcit | Rodae |
| Olten | Olten |
| Olusẹgun Ọbasanjọ | Olusegun Obasanjo |
| Olympia | Olympia |
| Olympiacos Pireus | Olympiakos Pireo |
| Olympiakos Nikozja | Olympiakos Nicosia |
| Olympiakos Pireus | Olympiakos Pireo |
| Olympiakos SFP | Olympiakos Pireo |
| Olympic Airlines | Olympic Airlines |
| Olympique Lyon | Olympique Lyonnais |
| Olympique Marsylia | Olympique Marsiglia |
| Olympos | Olimpo |
| Olympus | Olympus |
| Olympus Mons | Olympus Mons |
| Olza | Alnus |
| Oléron | Oléron |
| Ol’šavce | Oľšavce |
| om | ohm |
| Om mani padme hum | Om mani padme hum |
| Omacnica prosowianka | Ostrinia nubilalis |
| Omacnicowate | Pyralidae |
| Omaha | Omaha |
| Oman | Oman |
| Omar | Omar |
| Omar al-Baszir | Omar Hassan Ahmad al-Bashir |
| Omar Bongo | Omar Bongo |
| Omar Bradley | Omar Bradley |
| Omar Chajjam | Omar Khayyam |
| Omar Hashim Epps | Omar Epps |
| Omar Mukhtar | Omar al-Mukhtar |
| Omar Pène | Omar Pène |
| Omar Sharif | Omar Sharif |
| Omar Sívori | Enrique Omar Sivori |
| Omari Tetradze | Omari Tetradze |
| omawiać | discutere |
| omdlenie | svenimento |
| Omdurman | Omdurman |
| Ome | Ome |
| omega | omega |
| Omega Centauri | Omega Centauri |
| OmegaWiki | OmegaWiki |
| Omegna | Omegna |
| Ometecuhtli | Ometecuhtli |
| Ometeotl | Ometeotl |
| Omfale | Onfale |
| Omikron | Omicron |
| Omloop Het Volk | Omloop Het Volk |
| omocznia | alantoide |
| Omoforion | Omoforio |
| Omomierz | Ohmetro |
| OMR | Optical mark recognition |
| Omsk | Omsk |
| Omskavia | Omskavia Airlines |
| Omuta | Ōmuta |
| on | egli |
| On an Island | On an Island |
| On the Night | On the Night |
| On Through The Night | On Through the Night |
| ON-Line System | ON Line System |
| ona | lei |
| Ona mnie nienawidzi | Lei mi odia |
| Onan | Onan |
| Onani | Onanì |
| onanizm | masturbazione |
| Once in a LIVEtime | Once in a LIVEtime |
| Oncilla | Leopardus tigrinus |
| Ondo | Ondo |
| Ondyna | Ondina |
| Ondyny | Ondina |
| one | loro |
| One by One | One by One |
| One Night Stand | WWE One Night Stand |
| One Piece | One Piece |
| One Step Closer | Crawling |
| Onega | Lago Onega |
| Onegai Teacher | Onegai Teacher |
| Onegai Twins | Onegai Twins |
| Onejromancja | Oniromanzia |
| Oneworld | Oneworld |
| Onex | Onex |
| oni | loro |
| Oni żyją | Essi vivono |
| oniemiały | ammutolito |
| Onix | Onix |
| Onkogen | Oncogene |
| Onkogeny | Oncogene |
| onkologia | oncologia |
| Online analytical processing | OLAP |
| Onnens | Onnens |
| Onomastyka | Onomastica |
| Onsen | Onsen |
| Onsernone | Onsernone |
| Ontario | Lago Ontario |
| ontogeneza | ontogenesi |
| ontologia | ontologia |
| ontologiczny | ontologico |
| Ontronik Khachaturian | Andy Khachaturian |
| ONUB | ONUB |
| ONZ | Organizzazione delle Nazioni Unite |
| OOBE | Esperienze extracorporee |
| Oocyt | Ovocita |
| Oogamia | Ooogamia |
| Oolity | Ooliti |
| Oorlans | Oorlans |
| OoSaint-Cappel | Oost-Cappel |
| OOŚ | VIA |
| Op-art | Op art |
| OPAC | OPAC |
| opactwo | abbazia |
| Opactwo Clairvaux | Abbazia di Clairvaux |
| Opactwo Cîteaux | Abbazia di Cîteaux |
| Opactwo Fontenay | Abbazia di Fontenay |
| Opactwo i klasztor Altenmünster w Lorsch | Abbazia di Lorsch |
| Opactwo Morimond | Abbazia di Morimond |
| Opactwo Thelemy | Abbazia di Thélema |
| Opactwo w Aurillac | Abbazia di Aurillac |
| Opactwo w Cluny | Abbazia di Cluny |
| Opactwo w Gigny | Abbazia di Gigny |
| Opactwo Westminsterskie | Abbazia di Westminster |
| Opad atmosferyczny | Precipitazione |
| opad chemiczny | fallout chimico |
| opad kwaśnego deszczu | deposizione acida |
| opad pyłu | fallout |
| opad zanieczyszczeń | deposizione di inquinanti |
| opad zanieczyszczeń z atmosfery | ricaduta atmosferica |
| opad śniegu | nevicata |
