| ostentar | prale |
| Osteoporosis | Osteoporose |
| Ostpolitik | Østpolitik |
| ostra | østers |
| Ostrava | Ostrava |
| ostricultura | østersbrug |
| Ostrogodos | Ostrogoterne |
| Ostsiedlung | Tysk kolonisering i middelalderen |
| osupljiv | forbløffende |
| Osvaldo Golijov | Osvaldo Golijov |
| Oswald Mosley | Oswald Mosley |
| OTAN | NATO |
| Otariidae | Øresæler |
| Otello | Otello |
| Otelo | Othello |
| Otocyon megalotis | Øreræv |
| Otoh Gunga | Otoh Gunga |
| otoño | efterår |
| otra | andre |
| otra vez | igen |
| otras | andre |
| otro | andre |
| otro yo | dobbeltgænger |
| otros | andre |
| Ottavio Bottecchia | Ottavio Bottecchia |
| Ottawa | Ottawa |
| Ottawa Senators | Ottawa Senators |
| Otto de Freising | Otto af Freising |
| Otto Hahn | Otto Hahn |
| Otto I de Saboya | Otto |
| Otto Jespersen | Otto Jespersen |
| Otto Klemperer | Otto Klemperer |
| Otto Lilienthal | Otto Lilienthal |
| Otto Mann | Otto |
| Otto Robert Frisch | Otto Robert Frisch |
| Otto Skorzeny | Otto Skorzeny |
| Otto von Bismarck | Otto von Bismarck |
| Otto von Guericke | Otto von Guericke |
| Otto von Spreckelsen | Johan Otto von Spreckelsen |
| Ottorino Respighi | Ottorino Respighi |
| Otus scops | Dværghornugle |
| Otón | Otho |
| Otón de Freising | Otto af Freising |
| Otón I de Alemania | Otto den Store |
| Otón IV de Brunswick-Grubenhagen | Otto |
| Oudenaarde | Oudenaarde |
| Ouija | Ouija |
| Oulu | Oulu |
| Outremer | Outremer |
| Outsourcing | Outsourcing |
| Ovamboland | Ovamboland |
| ovario | æggestok |
| oveja | får |
| Oveja Dolly | Fåret Dolly |
| oveja madre | moderfår |
| oveja negra | sort får |
| ovejero | fårehyrde |
| Overclock | Overclocking |
| Overol | Hel |
| Overijssel | Overijssel |
| Ovibos moschatus | Moskusokse |
| Ovidio | Publius Ovidius Naso |
| ovino | får |
| OVNI | Ufo |
