| Oktoberfest | Oktoberfest |
| Oktyabrsky | Oktjabrski |
| Okulovka | Okoelovka |
| Ol Doinyo Lengai | Ol Doinyo Lengai |
| Olaberria | Olaberria |
| Olaf I | Olaf I |
| Olaf I of Denmark | Olaf I van Denemarken |
| Olaf I of Norway | Olaf I van Noorwegen |
| Olaf II of Norway | Olaf II van Noorwegen |
| Olaf III of Norway | Olaf III van Noorwegen |
| Olaf Magnusson of Norway | Olaf Magnusson |
| Olancho | Olancho |
| Olang | Olang |
| Olanzapine | Olanzapine |
| OLAP cube | Cube |
| Olaus Magnus | Olaus Magnus |
| Olav | Olof II van Zweden |
| Olav IV of Norway | Olaf IV van Noorwegen |
| Olav V of Norway | Olaf V van Noorwegen |
| Olavarría Partido | Olavarría |
| Olavinlinna | Olavinlinna |
| Olbendorf | Olbendorf |
| Olbernhau | Olbernhau |
| Olbersleben | Olbersleben |
| Olbia | Olbia |
| Olching | Olching |
| old | oud |
| Old Acquaintance | Old Acquaintance |
| old age | ouderdom |
| Old Believers | Oudgelovigen |
| Old Catholic Church | Oud-katholieke Kerk |
| Old Catholic Church of Austria | Oud-katholieke Kerk |
| Old Catholic Mission in France | Oud-katholieke Kerk |
| Old Church Slavonic | Oudkerkslavisch |
| Old City | Oude Stad |
| Old City of Jerusalem | Oude Stad |
| Old Dominion | Virginia |
| Old Dutch | Oudnederlands |
| Old East Slavic | Oudrussisch |
| Old English | Oudengels |
| Old English language | Oudengels |
| Old European Script | Vinča-cultuur |
| Old Faithful Geyser | Old Faithful |
| Old Firm | The Old Firm |
| old folks' home | bejaardenhuis |
| Old French | Oudfrans |
| Old Frisian | Oudfries |
| Old Great Bulgaria | Groot-Bulgaarse Rijk |
| Old Greek | Helleens |
| Old High German | Oudhoogduits |
| Old Indian Defense | Schaakopening - Oud Indisch |
| Old King Cole | Old King Cole |
| Old Kingdom | Oude Rijk |
| Old Man and the Sea | De oude man en de zee |
| Old Norse | Oudnoords |
| Old Norse language | Oudnoords |
| Old Nosy | Wellington |
| Old Novgorod dialect | Oudnovgorods |
| old people's home | bejaardenhuis |
| Old Prussia | Pruisen |
| Old Prussian | Oud-Pruisisch |
| Old Prussians | Pruisen |
| Old Saxon | Oudsaksisch |
| Old school hip hop | Old school hiphop |
| Old Shatterhand | Old Shatterhand |
| Old Slavic | Oudkerkslavisch |
| Old Street station | Station Old Street |
| Old Testament | Oude Testament |
| Old Town of Prague | Oude Stad |
| Old Town Square | Oudestadsplein |
| Old Trafford | Old Trafford |
| Old Tupi language | Tupi |
| Old Vic | Old Vic |
| Old World | Oude Wereld |
| Old World flycatcher | Vliegenvangers |
| Old World monkey | Apen van de Oude Wereld |
| Old World porcupine | Stekelvarkens van de Oude Wereld |
| Old World Swallowtail | Koninginnenpage |
| Old World warbler | Zangers van de Oude Wereld |
| old-established | gevestigd |
| old-fashioned | verouderd |
| Old-house borer | Huisboktor |
| old-time | oud |
| old-timer | oldtimer |
| Oldboy | Oldboy |
| Oldenburg | Oldenburg |
| Oldendorf | Oldendorf |
