| Ontronik Khachaturian | Ontronik Khachaturian |
| Onufry Kopczynski | Onufry Kopczyński |
| Onuphrius | Święty Onufry |
| onus | obowiązek |
| Onychomycosis | Grzybica paznokci |
| OODA Loop | OODA |
| oodh | agar |
| Oogamy | Oogamia |
| Oogonium | Lęgnia |
| oohing and ahhing | achy i ochy |
| Oolite | Oolity |
| Oology | Owologia |
| Oomiac | Umiak |
| Oomiak | Umiak |
| Oomoto | Oomoto |
| Oomycete | Lęgniowce |
| Ooogamy | Oogamia |
| Oorlans | Oorlans |
| Oort cloud | obłok Oorta |
| Oostende | Ostenda |
| Oosterpark Stadion | Oosterpark Stadion |
| Ootacamund | Utakamand |
| OP | PO |
| Opabinia | Opabinia |
| OPAC | OPAC |
| opal | opal |
| Opalenica | Opalenica |
| Opatija | Opatija |
| Opatów | Opatów |
| Opatów County | Powiat opatowski |
| Opava | Opawa |
| Opava District | Powiat Opawa |
| Opava River | Opawa |
| Opchanacanough | Opchanacanough |
| OPEC | OPEC |
| Opel | Adam Opel AG |
| Opel Antara | Opel Antara |
| Opel Astra | Opel Astra |
| Opel Corsa | Opel Corsa |
| Opel Kadett | Opel Kadett |
| Opel Meriva | Opel Meriva |
| Opel Senator | Opel Senator |
| Opel Vectra | Opel Vectra |
| Opel Zafira | Opel Zafira |
| open | otwarcie |
| Open and closed maps | Odwzorowanie otwarte |
| Open back rounded vowel | Samogłoska otwarta tylna zaokrąglona |
| Open back unrounded vowel | Samogłoska otwarta tylna niezaokrąglona |
| Open bog | Newa |
| Open bolt | Zamek swobodny |
| Open Clip Art Library | Wolna biblioteka klipartów |
| Open cluster | Gromada otwarta |
| Open content | Wolna dokumentacja |
| Open Data-Link Interface | Open Data-Link Interface |
| Open Database Connectivity | ODBC |
| Open de Moselle | Open de Moselle |
| Open de Tenis Comunidad Valenciana | Open de Tenis Comunidad Valenciana |
| Open Directory Project | Open Directory Project |
| Open front rounded vowel | Samogłoska otwarta przednia zaokrąglona |
| Open front unrounded vowel | Samogłoska otwarta przednia niezaokrąglona |
| Open Gaz de France | Open Gaz de France |
| Open Graphics Project | Open Graphics Project |
| Open hearth furnace | Piec martenowski |
| Open Innovation | Open Innovation |
| Open Invention Network | Open Invention Network |
| open lawn | trawniki |
| open letter | list otwarty |
| Open Lock | Lockpicking |
| Open mail relay | Open relay |
| Open out | Otwieraă |
| Open problem | Problem otwarty |
| Open proxy | Open proxy |
| Open reading frame | Otwarta ramka odczytu |
| Open Romania | BCR Open Romania |
| open sea | otwarte morze |
| open sea fishing | rybołówstwo dalekomorskie |
| Open SEAT | Open Seat |
| Open set | Zbiór otwarty |
| Open Society Institute | Open Society Institute |
| Open Sound System | Open Sound System |
| Open source | Otwarte oprogramowanie |
| Open Source Definition | Definicja Otwartego Źródła |
| Open Source Development Labs | Open Source Development Labs |
| Open source software | Otwarte oprogramowanie |
| Open standard | Otwarty standard |
| Open star cluste | Gromada otwarta |
| Open star cluster | Gromada otwarta |
| Open star clusters | Gromada otwarta |
