| opale | opal |
| opalescence | opalescence |
| opalescent | opalescent |
| opaque | opaque |
| Opatija | Opatija |
| Opava | Opava |
| Opchanacanough | Opchanacanough |
| Opel | Opel |
| Opel Astra G | General Motors Astra |
| Opel Astra H | General Motors Astra |
| Opel Corsa | Opel Corsa |
| Opel Meriva | Opel Meriva |
| Opel Vectra | Opel Vectra |
| Opel Zafira | Opel Zafira |
| Open Arena | OpenArena |
| Open Canvas | OpenCanvas |
| Open Clip Art Library | Open Clip Art Library |
| Open database connectivity | Open Database Connectivity |
| Open de Bangalore | Bangalore Open |
| Open de Barcelone | Open SEAT |
| Open de Bois-le-Duc | Ordina Open |
| Open de Bombay | Kingfisher Airlines Tennis Open |
| Open de Bâle | Davidoff Swiss Indoors |
| Open de Chennai | Chennai Open |
| Open de Chine | China Open |
| Open de Corée | Hansol Korea Open Tennis Championships |
| Open de Croatie Umag | Croatia Open Umag |
| Open de Doha | Qatar ExxonMobil Open |
| Open de Dubaï | Dubai Tennis Championships |
| Open de France de badminton | French Open |
| Open de Gstaad | Allianz Suisse Open Gstaad |
| Open de Halle | Gerry Weber Open |
| Open de Kitzbühel | Austrian Open |
| Open de Las Vegas | Tennis Channel Open |
| Open de Los Angeles | East West Bank Classic |
| Open de Moselle | Open de Moselle |
| Open de Munich | Munich Open |
| Open de Nottingham | Nottingham Open |
| Open de Palermo | Palermo Open |
| Open de Prague | ECM Prague Open |
| Open de Roumanie | Open Romania |
| Open de Russie | Imperial Collection Russian Open |
| Open de Saint-Omer | Open de Saint-Omer |
| Open de San José | SAP Open |
| Open de Sicile | Campionati Internazionali di Sicilia |
| Open de Slovénie | Banka Koper Slovenia Open |
| Open de Suède | Swedish Open |
| Open de Tachkent | Tashkent Open |
| Open de Tel Aviv | Anda Open |
| Open de Thaïlande | Thailand Open |
| Open de Tōkyō | Toray Pan Pacific Open |
| Open de Valence | Open de Tenis Comunidad Valenciana |
| Open de Viña del Mar | Movistar Open |
| Open de Zurich | Zurich Open |
| Open Directory Project | Open Directory Project |
| Open du Brésil | Brasil Open |
| Open du Japon | Japan Open Tennis Championships |
| Open du Mexique | Abierto Mexicano Telcel |
| Open européen | European Open |
| Open Gaz de France | Open Gaz de France |
| Open Group | The Open Group |
| Open invention network | Open Invention Network |
| Open Motif | Open Motif |
| Open Sound System | Open Sound System |
| Open Source | Open source |
| Open Source Definition | Open Source Definition |
| Open Source Development Labs | Open Source Development Labs |
| Open University | Open University |
| Open XML | Office Open XML |
| Open your eyes | Open Your Eyes |
| Open Your Heart | Open Your Heart |
| Open-jaw | Open-jaw ticket |
| OpenCourseWare | MIT OpenCourseWare |
| OpenGL user interface library | OpenGL User Interface Library |
| OpenGL utility library | OpenGL Utility Library |
| OpenGL utility toolkit | OpenGL Utility Toolkit |
| OpenGraphics | Open Graphics Project |
| OpenLaszlo | OpenLaszlo |
| OpenMosix | OpenMosix |
| OpenNap | Opennap |
| OpenSolaris | OpenSolaris |
| OPENSTEP | OpenStep |
| OpenSUSE | OpenSUSE |
| OpenVPN | OpenVPN |
| OpenWrt | OpenWrt |
| OPEP | OPEC |
| Opera | Opera |
| Opera Garnier | Palais Garnier |
| Opera Nazionale Balilla | Opera Nazionale Balilla |
| Opera seria | Opera seria |
| Opera Software | Opera Software |
| Operación Triunfo | Operación Triunfo |
| Operation Barbarossa | Operation Barbarossa |
| Operation Ivy | Operation Ivy |
| Operation Wolf | Operation Wolf |
| Opfertshofen | Opfertshofen |
| Opfikon | Opfikon |
| Ophel | Ophel |
| Opheodrys | Opheodrys |
| Ophichthidae | Ophichthidae |
| ophicéphale | snakehead |
| Ophidiiformes | Ophidiiformes |
| Ophioglossaceae | Ophioglossaceae |
| Ophioglossales | Ophioglossales |
| Ophioglosse commun | Ophioglossum vulgatum |
| Ophioglossophyta | Ophioglossophyta |
| Ophioglossum | Ophioglossum |
| Ophiolite | Ophiolite |
| Ophion | Ophion |
| Ophir | Ophir |
| Ophites | Ophites |
| Ophiuchus | Ophiuchus |
| Ophrys abeille | Bee Orchid |
| Ophrys apifera | Ophrys apifera |
| Ophrys araignée | Ophrys sphegodes |
| Ophrys bécasse | Ophrys scopolax |
| Ophrys de Gascogne | Ophrys vasconica |
| Ophrys de Provence | Ophrys provincialis |
| Ophrys jaune | Ophrys lutea |
| Ophrys petite araignée | Ophrys araneola |
| Ophrys tenthredinifera | Ophrys tenthredinifera |
| ophtalmique | ophthalmic |
| ophtalmo | ophthalmologist |
| ophtalmologie | ophthalmology |
| ophthalmologiste | ophthalmologist |
| ophthalmologue | ophthalmologist |
