| onödig | unødvendig |
| oordning | uorden |
| oorganisk förorening | uorganisk forurenende stof |
| oorganisk kemi | uorganisk kemi |
| oorganiskt gödselmedel | kunstgødning |
| oortodox | uortodoks |
| Oorts kometmoln | Oortskyen |
| Oostende | Oostende |
| opassande | dårlig |
| opastöriserad | upasteuriseret |
| Opatija | Opatija |
| OPEC | OPEC |
| Opel | Opel |
| Opel Corsa | Opel Corsa |
| Open Directory Project | Open Directory Project |
| Open Shortest Path First | OSPF |
| Open Systems Interconnection | OSI-model |
| OpenSUSE | OpenSUSE |
| OpenVPN | OpenVPN |
| opera | opera |
| Opera -n | Opera |
| Opera metal | Symfonisk metal |
| Operaen på Holmen | Operaen på Holmen |
| Operahuset i Sydney | Sydney Opera House |
| Operation -en -er | Operation |
| Operation Barbarossa | Operation Barbarossa |
| Operation Entebbe | Operation Entebbe |
| Operation Greif | Operation Greif |
| Operation Merkur | Slaget om Kreta |
| Operation Overlord | Operation Overlord |
| Operation Panzerfaust | Operation Panzerfaust |
| Operation Stösser | Operation Stösser |
| Operation Torch | Operation Torch |
| Operation Vigilant Resolve | Operation Vigilant Resolve |
| Operation Weserübung | Operation Weserübung |
| Operationsförstärkare | Operationsforstærker |
| Operationssystem | Styresystem |
| operativsystem | styresystem |
| Operativsystemkärna | Kerne |
| Operatorprioritet | Operatorprioritet |
| operett | operette |
| Ophelia | Ophelia |
| Opievallmo | Opiumvalmue |
| opinionsundersökning | markedsforskning |
| Opioid | Opioid |
| opium | opium |
| Opiumkrigen | Opiumskrigene |
| Opkonst | Op art |
| Opole | Opole |
| Opole vojvodskap | Opole |
| Oppdal kommun | Oppdal |
| Oppegård kommun | Oppegård |
| Oppfinnar-Jocke | Georg Gearløs |
| Oppland fylke | Oppland |
| Oprah Winfrey | Oprah Winfrey |
