| Original sin | Izvirni greh |
| Origins of Prussia | Prusija |
| Origins of the American Civil War | Ameriška državljanska vojna |
| Orion | Orion |
| Orion Nebula | Orionova meglica |
| Orlande de Lassus | Orlando di Lasso |
| Orleans | Orléans |
| Orlice | Adler |
| Orléanais | Orléanais |
| Orléans | Orléans |
| Ormož | Občina Ormož |
| Orne | Orne |
| Orne River | Orne |
| ornithology | ornitologija |
| Orobanchaceae | Pojalnikovke |
| orography | orografija |
| Orologio | Ura |
| Oromë | Oromë |
| Oropher | Oropher |
| Orphan drug | Zdravilo sirota |
| Orphans of the Sky | Vesolje |
| Orson Welles | Orson Welles |
| Orthodox | Pravoslavje |
| Orthodox Christianity | Pravoslavje |
| Orthodrome | Veliki krog |
| orthography | pravopis |
| Orthopedic cast | Mavec |
| Orthopedic surgery | Ortopedija |
| Orthoptera | Kobilice |
| orthopteran | ravnokrilci |
| Orthosie | Ortozija |
| Oryol | Aquila |
| Oryza | Riž |
| OS | Operacijski sistem |
| Osama bin Laden | Osama bin Laden |
| Osborne Reynolds | Osbourne Reynolds |
| Oscan language | Oskijščina |
| Oscar | Oskar |
| Oscar Alfredo Gálvez | Oscar Alfredo Gálvez |
| Oscar class submarine | Oskar |
| Oscar Luigi Scalfaro | Oscar Luigi Scalfaro |
| Oscar Wilde | Oscar Wilde |
| Osco | Oskijščina |
| Osella | Osella |
| Osijek | Osijek |
| Osijek-Baranja County | Osiješko-baranjska županija |
| Osilnica | Občina Osilnica |
| Osip Mandelstam | Osip Mandelštam |
| Osirak | Operacija Opera |
| Osiris | Oziris |
| Osiris Shoes | Oziris |
| Oskar Backlund | Johan Oskar Backlund |
| Oskar Schindler | Oskar Schindler |
| Oslo | Oslo |
| osmium | osmij |
| osmosis | osmoza |
| Osnabrück | Osnabrück |
| Osor | Osor |
| Osprey | Ribji orel |
| Ossetia | Južna Osetija |
| Ossiach | Osoje |
| Osteichthyes | Ribe |
| Osten | Vzhod |
| Osteoporosis | Osteoporoza |
| Osterøy | Osterøy |
| Ostia | Hostija |
| ostrich | noj |
| Ostrov | Otok |
| Osvaldo Dorticós Torrado | Osvaldo Dorticós Torrado |
| Oswaldo Aranha | Oswaldo Aranha |
| Oswiecim | Auschwitz |
| OT | OT |
| Otava River | Ottawa |
| Otello | Othello |
| Othello | Othello |
| other | drugi |
