| oordning | Aufruhr |
| Oordning -en | Durcheinander |
| oorganiserad | unorganisiert |
| oorganisk | unorganisch |
| oorganisk förorening | anorganischer Schadstoff |
| oorganisk kemi | Anorganik |
| oorganiskt gödselmedel | Mineraldünger |
| oortodox | unorthodox |
| Oorts kometmoln | Oortsche Wolke |
| Oostende | Ostende |
| Opabinia | Opabinia |
| opaion | Auge |
| opak | lichtundurchlässig |
| opal | Opal |
| opalescens | Opalisieren |
| opalskimrande | opalisierend |
| opartisk | gerecht |
| opartiskhet | Unparteilichkeit |
| opassande | unverschämt |
| opassande beteende | Ungehörigkeit |
| opassande förslag | anstößiger Antrag |
| opasslig | marode |
| Opatija | Opatija |
| OPC | OLE for Process Control |
| OPEC | OPEC |
| Opel | Opel |
| Opel Antara | Opel Antara |
| Opel Corsa | Opel Corsa |
| Opel Frontera | Opel Frontera |
| Opel Meriva | Opel Meriva |
| Opel Senator | Opel Senator |
| Opel Vectra | Opel Vectra |
| Opel Zafira | Opel Zafira |
| Open Directory Project | Open Directory Project |
| Open Enterprise Server | Open Enterprise Server |
| Open Shortest Path First | Open Shortest Path First |
| Open Sound System | Open Sound System |
| Open Source Development Labs | Open Source Development Labs |
| Open Systems Interconnection | OSI-Modell |
| Open University | Open University |
| Open Water | Open Water |
| OpenArena | OpenArena |
| Openbox | Openbox |
| OpenSolaris | OpenSolaris |
| OPENSTEP | OpenStep |
| OpenSUSE | OpenSuse |
| OpenVMS | Virtual Memory System |
| OpenVPN | OpenVPN |
| opera | Oper |
| Opera -n | Oper |
| Opera buffa | Opera buffa |
| Opera metal | Symphonic Metal |
| opera- | Opern- |
| operabel | operabel |
| Operación Puerto | Dopingskandal Fuentes |
| Operaen på Holmen | Königliche Oper |
| Operahuset i Sydney | Sydney Opera House |
| operation | chirurgische Eingriff |
| Operation -en -er | Operation |
| Operation Achilles | Operation Achilles |
| Operation Ajax | Operation Ajax |
| Operation Bagration | Operation Bagration |
| Operation Barbarossa | Unternehmen Barbarossa |
| Operation Blå | Operation Blau |
| Operation Condor | Operation Condor |
| Operation Dragoon | Operation Dragoon |
| Operation Dynamo | Operation Dynamo |
| Operation Entebbe | Operation Entebbe |
| Operation Fenix | Operation Phoenix |
| Operation Flashpoint | Operation Flashpoint |
| Operation Frühlingserwachen | Plattenseeoffensive |
| Operation Greif | Unternehmen Greif |
| Operation Highjump | Operation Highjump |
| Operation Husky | Operation Husky |
| Operation Ivy | Operation Ivy |
| Operation kjoltyg | Unternehmen Petticoat |
| Operation Market Garden | Operation Market Garden |
| Operation Mars | Operation Mars |
| Operation Merkur | Luftlandeschlacht um Kreta |
| Operation Neptune | Operation Neptune |
| Operation Nordwind | Operation Nordwind |
| Operation Northwoods | Operation Northwoods |
| Operation Overlord | Operation Overlord |
| Operation Reinhard | Aktion Reinhardt |
| Operation Rösselsprung | Operation Rösselsprung |
| Operation Seelöwe | Unternehmen Seelöwe |
| Operation Sledgehammer | Operation Sledgehammer |
| Operation Sommarregn | Operation Sommerregen |
| Operation Stella Polaris | Operation Stella Polaris |
| Operation Storm | Militäroperation Oluja |
| Operation Tannenbaum | Operation Tannenbaum |
| Operation Tannenberg | Unternehmen Tannenberg |
| Operation Torch | Operation Torch |
| Operation Vigilant Resolve | Operation Vigilant Resolve |
| Operation Weserübung | Unternehmen Weserübung |
| Operations Support System | Operations Support System |
| Operationsförstärkare | Operationsverstärker |
| Operationssystem | Betriebssystem |
| operationsverktyg | Besteck |
| operativsystem | Betriebssystem |
| Operativsystemkärna | Betriebssystemkern |
| Operator | Operator |
| Operatorprioritet | Operatorrangfolge |
| operatris | Maschinenbedienerin |
