| Orphans of the Sky | Wszechświat |
| Orpheus | Orfeusz |
| Orphism | Orfizm |
| Orquesta típica | Orquesta típica |
| Orrin Hatch | Orrin Hatch |
| Orrorin tugenensis | Orrorin |
| Orsa Municipality | Gmina Orsa |
| Orsanmichele | Orsanmichele |
| Orselina | Orselina |
| Orsha | Orsza |
| Orsingen-Nenzingen | Orsingen-Nenzingen |
| Orsini | Giordano Orsini |
| Orsini family | Giordano Orsini |
| Orsières | Orsières |
| Orsk | Orsk |
| Orso II Participazio | Orso II Partecipazio |
| Orso Ipato | Orso Ipato |
| Orson Hodge | Orson Hodge |
| Orson Scott Card | Orson Scott Card |
| Orson Welles | Orson Welles |
| Ort | Ort |
| Ortac | Ortac |
| Ortenaukreis | Powiat Ortenau |
| Ortenburg | Ortenburg |
| Orthanc | Orthank |
| Orthez | Orthez |
| orthodox | konserwatywny |
| Orthodox Church of Constantinople | Patriarcha Konstantynopola |
| Orthodox Patriarch of Jerusalem | Prawosławny patriarchat Jerozolimy |
| orthodox priest | pop |
| Orthodrome | Koło wielkie |
| Orthogastropoda | Ślimak winniczek |
| Orthogonal complement | Dopełnienie zbioru |
| Orthogonal frequency-division multiplexing | OFDM |
| Orthogonal matrix | Macierz ortogonalna |
| orthography | ortografia |
| Orthomyxoviridae | Ortomyksowirusy |
| Orthonectida | Prostopływce |
| Orthonormal basis | Baza ortonormalna |
| Orthonormality | Funkcje ortonormalne |
| Orthonychidae | Ziemnodrozdy |
| Orthopantomogram | Pantomogram |
| Orthopedic cast | Gładź szpachlowa |
| Orthopedic surgery | Ortopedia |
| Orthophoto | Ortofotomapa |
| orthopteran | prostoskrzydłe |
| Orthorexia nervosa | Ortoreksja |
| Orthorhombic crystal system | Układ rombowy |
| orthortopic | ortotropowy |
| Orthosie | Orthosie |
| Orthrus | Ortros |
| Ortler | Ortler |
| Ortler Alps | Ortler |
| Ortoncone | Stożki Segera |
| Ortuťová | Ortut’ová |
| Oruchuban Ebichu | Oruchuban Ebichu |
| Oruro Department | Oruro |
| Orust Municipality | Gmina Orust |
| Orvar Bergmark | Orvar Bergmark |
| Orvieto | Orvieto |
| Orville Turnquest | Orville Alton Turnquest |
| Orville Wright | Bracia Wright |
| Oryctodromeus | Oryktodrom |
| Oryctolagus | Królik domowy |
| Oryol | Orzeł |
| Oryol Oblast | Obwód orłowski |
| Oryzias latipes | Adrianichthyidae |
| Orzens | Orzens |
| Orzesze | Orzesze |
| Orzinuovi | Orzinuovi |
| Orzysz | Orzysz |
| Orăştie | Orăştie |
| Orşova | Orşova |
| OS | System operacyjny |
| Os Pinos | Hymn Galicii |
| Osadné | Osadné |
| Osage County | Hrabstwo Osage |
| Osaka | Osaka |
| Osaka Bay | Zatoka Osaka |
| Osaka Castle | Osaka |
| Osaka International Airport | Port lotniczy Ōsaka |
| Osaka Monorail | Osaka Monorail |
| Osaka Municipal Subway | Metro w Osace |
| Osaka Prefecture | Prefektura Ōsaka |
| Osam | Osym |
| Osama bin Laden | Usama ibn Ladin |
| Osan | Osan |
| Osborne House | Osborne House |
| Osborne Reynolds | Osborne Reynolds |
| Osbourne Fleming | Osbourne Fleming |
| Osby Municipality | Gmina Osby |
| Oscan language | Język oskijski |
| Oscar | Pielęgnica pawiooka |
| Oscar Alberto Ortiz | Oscar Alberto Ortiz |
| Oscar Camenzind | Oscar Camenzind |
| Oscar de la Hoya | Oscar de la Hoya |
| Oscar Hammerstein II | Oscar Hammerstein II |
| Oscar I of Sweden | Oskar I |
| Oscar II of Sweden | Oskar II |
| Oscar Luigi Scalfaro | Oscar Luigi Scalfaro |
| Oscar Milosz | Oskar Miłosz |
| Oscar Montelius | Gustaw Oscar Montelius |
| Oscar Míguez | Oscar Míguez |
| Oscar Niemeyer | Oscar Niemeyer |
| Oscar Panno | Óscar Panno |
| Oscar Peterson | Oscar Peterson |
| Oscar Robertson | Oscar Robertson |
| Oscar Ruggeri | Oscar Ruggeri |
| Oscar Tabárez | Oscar Tabárez |
| Oscar Temaru | Oscar Temaru |
| Oscar Troplowitz | Oskar Troplowitz |
| Oscar Ustari | Óscar Ustari |
| Oscar Wilde | Oscar Wilde |
| Osceola County | Hrabstwo Osceola |
| Oschatz | Oschatz |
| Osci | Oskowie |
| Oscillation | Drgania |
| Oscillatoria | Drgalnica |
| Osco | Osco |
| Osco-Umbrian languages | Języki oskijsko-umbryjskie |
| Ose | Eza |
| Osechi | Osechi ryori |
| Osei Kofi Tutu I | Osei Tutu |
| Oseltamivir | Oseltamiwir |
| Osen | Osen |
| Osgiliath | Osgiliath |
| Osgood-Schlatter disease | Choroba Osgooda-Schlattera |
| Osh Province | Obwód oszyński |
| Oshawa Generals | Oshawa Generals |
| Oshima Peninsula | Półwysep Oshima |
| Oshiwambo language | Język ndonga |
| OSI | Office of Strategic Influence |
| OSI model | Model OSI |
| Osieczna | Osieczna |
| Osiek | Osiek |
| Osijek | Osijek |
| Osijek-Baranja County | Osijecko-barańska żupa |
| Osip Mandelstam | Osip Mandelsztam |
| Osiris | Ozyrys |
| Osiris Shoes | Ozyrys |
| Oskar Barnack | Oskar Barnack |
| Oskar Davičo | Oskar Davičo |
| Oskar Dirlewanger | Oskar Dirlewanger |
| Oskar Klein | Oskar Klein |
| Oskar Kokoschka | Oskar Kokoschka |
| Oskar Lafontaine | Oskar Lafontaine |
| Oskar Schindler | Oskar Schindler |
| Oskarshamn Municipality | Gmina Oskarshamn |
| Oskemen | Öskemen |
| Oskol River | Oskoł |
| Oslo | Oslo |
