| opera- | operatic |
| Operabal | Vienna Opera Ball |
| operabel | operable |
| Operación Puerto | Operación Puerto doping case |
| Operación Triunfo | Operación Triunfo |
| Operagebouw | Opera |
| Operagebouw van Kopenhagen | Copenhagen Opera House |
| operatekst | booklet |
| operateur | projectionist |
| operatie | activity |
| Operatie Amherst | Operation Amherst |
| Operatie Anthropoid | Operation Anthropoid |
| Operatie Auca | Operation Auca |
| Operatie Barbarossa | Operation Barbarossa |
| Operatie Battleaxe | Operation Crusader |
| Operatie Bluecoat | Operation Bluecoat |
| Operatie Brevity | Operation Brevity |
| Operatie Chastise | Operation Chastise |
| Operatie Chicago | Mission Chicago |
| Operatie Cobra | Operation Cobra |
| Operatie Condor | Operation Condor |
| Operatie Crusader | Operation Crusader |
| Operatie Dagen van Boetedoening | Operation Days of Penitence |
| Operatie Desert Fox | Bombing of Iraq |
| Operatie Detroit | Mission Detroit |
| Operatie Dragoon | Operation Dragoon |
| Operatie Dynamo | Operation Dynamo |
| Operatie Fall Blau | Case Blue |
| Operatie Fall Gelb | Battle of France |
| Operatie Fall Grün | Fall Grün |
| Operatie Fall Rot | Operation Fall Rot |
| Operatie Fall Weiss | Fall Weiß |
| Operatie Fortitude | Operation Fortitude |
| Operatie Freshman | Norwegian heavy water sabotage |
| Operatie Gladio | Operation Gladio |
| Operatie Greif | Operation Greif |
| Operatie Herbstreise | Operation Herbstreise |
| Operatie Herfstwolken | Operation Autumn Clouds |
| Operatie Himmler | Gleiwitz incident |
| Operatie Just Cause | United States invasion of Panama |
| Operatie Lüttich | Operation Lüttich |
| Operatie Market Garden | Operation Market Garden |
| Operatie Mobilisatie | Operation Mobilisation |
| Operatie Paukenschlag | Second Happy Time |
| Operatie Plunder | Operation Plunder |
| Operatie Pluto | Operation Pluto |
| Operatie Polarfuchs | Operation Arctic Fox |
| Operatie Seelöwe | Operation Sealion |
| Operatie Sledgehammer | Operation Sledgehammer |
| Operatie Storm | Operation Storm |
| Operatie Toorts | Operation Torch |
| Operatie Typhoon | Battle of Moscow |
| Operatie Uranus | Operation Uranus |
| Operatie Walküre | Operation Walküre |
| Operatie Weserübung | Operation Weserübung |
| operatiekoorts | surgical fever |
| Operation Ivy | Operation Ivy |
| Operation Paget | Operation Paget |
| Operation Southern Watch | Maritime Interdiction Operations |
| operationeel | operational |
| Operations management | Operations management |
| Operator-overloading | Operator overloading |
| Operatorentheorie | Operator theory |
| operatrice | projectionist |
| Operaïsme | Workerism |
| Operculum | Gill-cover |
| opereerbaar | operable |
| opereren | operate |
| operette | operetta |
| Opet-festival | Opet Festival |
| opeten | finish |
| Opfenbach | Opfenbach |
| Opfertshofen | Opfertshofen |
| Opfikon | Opfikon |
