| o ... o | either ... or |
| O Broadcasting System | O Broadcasting System |
| O Canada | O Canada |
| o exclusivo | exclusive or |
| O Holy Night | O Holy Night |
| o sea | that is to say |
| O Sul é o Meu País | O Sul é Meu País |
| O-Bahn Busway | O-Bahn Busway |
| O-Zone | O-Zone |
| O.T.A.N. | NATO |
| Oahu | Oahu |
| Oak Ridge National Laboratory | Oak Ridge National Laboratory |
| Oakland | Oakland |
| Oakland Athletics | Oakland Athletics |
| Oakland Raiders | Oakland Raiders |
| oasis | oasis |
| Oasis de Huacachina | Huacachina |
| Oaxaca | Oaxaca |
| Obalno-kraška | Obalno-kraška |
| Obatala | Obatala |
| Obatzda | Obatzda |
| Obbá | Oba |
| OBD | On-Board Diagnostics |
| Obdulio Varela | Obdulio Varela |
| Obdurodon | Obdurodon |
| Obed | Obed |
| obedecer | mind |
| obediencia | compliance |
| obediente | well-behaved |
| obedientemente | obediently |
| obelisco | obelisk |
| Obelisco de Buenos Aires | Obelisk of Buenos Aires |
| Oben am jungen Rhein | Oben am jungen Rhein |
| Oberbalm | Oberbalm |
| Oberbergischer Kreis | Oberbergischer Kreis |
| Oberbipp | Oberbipp |
| Oberbuchsiten | Oberbuchsiten |
| Oberburg | Oberburg |
| Oberbüren | Oberbüren |
| Oberdiessbach | Oberdiessbach |
| Oberegg | Oberegg |
| Oberems | Oberems |
| Obergerlafingen | Obergerlafingen |
| Obergesteln | Obergesteln |
| Oberhausen | Oberhausen |
| Oberhofen am Thunersee | Oberhofen am Thunersee |
| Oberhünigen | Oberhünigen |
| Oberiberg | Oberiberg |
| Oberland bernés | Bernese Oberland |
| Oberlangenegg | Oberlangenegg |
| Oberramsern | Oberramsern |
| Oberried am Brienzersee | Oberried am Brienzersee |
| Oberriet | Oberriet |
| Obersaxen | Obersaxen |
| Oberscharführer | Oberscharführer |
| Obersteckholz | Obersteckholz |
| Oberstocken | Oberstocken |
| Oberto | Oberto |
| obertura | overture |
| Obertura Coriolano | Coriolan Overture |
| Oberurnen | Oberurnen |
| Oberuzwil | Oberuzwil |
| Oberwil bei Büren | Oberwil bei Büren |
| Oberwil im Simmental | Oberwil im Simmental |
| Oberá | Oberá |
| Oberägeri | Oberägeri |
| Oberón | Oberon |
| Oberönz | Oberönz |
| Oberösch | Oberösch |
| obesidad | corpulence |
| obeso | corpulent |
| Obex | OBEX |
| Obi-Wan Kenobi | Obi-Wan Kenobi |
| obispado | bishopric |
| Obispado de Urgel | Diocese of Urgell |
| obispo | bishop |
| Obispo auxiliar | Auxiliary bishop |
| Obispo coadjutor | Coadjutor bishop |
| Obispo de Urgell | Bishop of Urgell |
| Obispo metropolitano | Metropolitan bishop |
| Obispos de Linköping | Bishop of Linköping |
| Obispos de Visby | Bishop of Visby |
| objecion | objection |
| objeción | contesting |
| objeción admitida | objection sustained |
