| ottusangolo | obtuse angled |
| ottusita | obtuseness |
| ottuso | blunt |
| Ottweiler | Ottweiler |
| Otus scops | European Scops Owl |
| Otxandio | Otxandio |
| Otzberg | Otzberg |
| Otzing | Otzing |
| OU | OU |
| Ouaddaï | Ouaddaï Region |
| Ouagadougou | Ouagadougou |
| Ouangani | Ouangani |
| Ouargla | Ouargla |
| Ouarzazate | Ouarzazate |
| Oud | Oud |
| Oudenaarde | Oudenaarde |
| Oudomxay | Oudomxai Province |
| Ouessant | Ushant |
| Ouest | West |
| Ouest Department | West |
| Ouguiya mauritana | Mauritanian ouguiya |
| OUI | OUI |
| Oulainen | Oulainen |
| Oulens-sous-Echallens | Oulens-sous-Echallens |
| Oulens-sur-Lucens | Oulens-sur-Lucens |
| Oulipo | Oulipo |
| Oullins | Oullins |
| Oulu | Oulu |
| Oulujoki | Oulujoki |
| Oulujärvi | Oulujärvi |
| Oulun | Oulun |
| Oulunsalo | Oulunsalo |
| Oungan | Houngan |
| Our Love to Admire | Our Love to Admire |
| Our Worlds at War | Our Worlds at War |
| Ouranosaurus nigeriensis | Ouranosaurus |
| Ourebia ourebi | Oribi |
| Ourengoï | Urengoy gas field |
| Ourense | Ourense |
| Ourique | Ourique |
| Ourne Valley | Ourne Valley |
| Ouro Preto | Ouro Preto |
| Ourscamp | Ourscamp |
| Ousmane Sembène | Ousmane Sembène |
| Outburst ottici | Optical outbursts |
| Outeniqua Choo Tjoe | Outeniqua Choo Tjoe |
| Outer Skerries | Out Skerries |
| OutKast | OutKast |
| Outlawz | Outlawz |
| Outlook Express | Outlook Express |
| output | output |
| Outremer | Outremer |
| outsider | underdog |
| ouverture | overture |
| Ouverture italiana | Italian overture |
| Ouviram do Ipiranga às margens plácidas | Hino Nacional do Brasil |
| Ouyang Xiu | Ouyang Xiu |
| Ouémé | Ouémé Department |
| OV | OV |
| ovaia | ovary |
| ovaio | ovary |
| ovale | egg-shaped |
| Ovale di Cassini | Cassini oval |
| Ovambo | Ovambo |
| Ovanåker | Ovanåker Municipality |
| Ovar | Ovar |
| ovarico | ovarian |
| ovariectomia | spay |
| ovario | ovary |
| ovatta | cotton |
| ovattare | pad |
