| ornamentation | adorno |
| ornamented in relief | grabado |
| ornate | recargar |
| Ornate Hawk-eagle | Spizaetus ornatus |
| ornateness | ahíto |
| Ornella Muti | Ornella Muti |
| Ornithischia | Ornithischia |
| Ornithogalum umbellatum | Ornithogalum umbellatum |
| Ornitholestes | Ornitholestes |
| ornithological | ornitológico |
| ornithologist | ornitólogo |
| ornithology | ornitología |
| Ornithomimidae | Ornithomimidae |
| Ornithomimosauria | Ornithomimidae |
| Ornithomimus | Ornithomimus |
| Ornithorhynchidae | Ornithorhynchidae |
| Orny | Orny |
| Oro Province | Provincia de Oro |
| Orobanchaceae | Orobanchaceae |
| Orochi | Orochi |
| Orochimaru | Orochimaru |
| Orodruin | Orodruin |
| Orographic lift | Nube orográfica |
| orography | orografía |
| Orologio | Reloj |
| Oromia Region | Oromia |
| Oromis | Oromis |
| Oromo | Oromo |
| Oromo language | Idioma oromo |
| Oromë | Oromë |
| Oron-la-Ville | Oron-la-Ville |
| Oron-le-Châtel | Oron-le-Châtel |
| Orona | Atolón Orona |
| Oronce Finé | Oronce Finé |
| Orontes River | Orontes |
| Oropesa District | Distrito de Oropesa |
| Oropeza Province | Oropeza |
| Oropos | Oropo |
| Oroqen | Oroqen |
| Oroquieta City | Oroquieta |
| Orosius | Paulo Orosio |
| Orosí Volcano | Volcán Orosí |
| Orotava Valley | Valle de La Orotava |
| Orozko | Orozco |
| orphan | huérfano |
| Orphan drug | Medicamento huérfano |
| orphanage | orfanato |
| Orphans of the Sky | Universo |
| Orphans of the Storm | Las dos huérfanas |
| Orpheus | Orfeo |
| Orphism | Orfismo |
| Orpund | Orpund |
| Orquesta Nacional de España | Orquesta Nacional de España |
| Orquesta Sinfónica de Galicia | Orquesta Sinfónica de Galicia |
| Orquesta típica | Orquesta típica |
| Orquestra Simfònica de Barcelona | Orquesta Sinfónica de Barcelona y Nacional de Cataluña |
| Orrorin tugenensis | Orrorin tugenensis |
| Orsanmichele | Iglesia de Orsanmichele |
| Orselina | Orselina |
| Orsha | Orsha |
| Orsini | Orsini |
| Orsini family | Orsini |
| Orsières | Orsières |
| Orso Ipato | Orso Ipato |
| Orson Hodge | Orson |
| Orson Scott Card | Orson Scott Card |
| Orson Welles | Orson Welles |
| Ort | ORT |
| Ortegal | Comarca de Ortegal |
| Ortegocactus macdougallii | Ortegocactus |
| Ortenaukreis | Distrito de Ortenau |
| Orthanc | Orthanc |
| orthoclase | adularia |
| orthodontics | ortodoncia |
| orthodox | ortodoxo |
| Orthodox Church in America | Iglesia Ortodoxa en América |
| Orthodox Church of Alexandria | Iglesia Ortodoxa de Alejandría |
| Orthodox Church of Constantinople | Iglesia Ortodoxa de Constantinopla |
| Orthodox Judaism | Judaísmo ortodoxo |
| orthodoxy | ortodoxia |
| Orthodrome | Gran círculo |
| Orthogastropoda | Orthogastropoda |
| Orthogonal coordinates | Coordenadas ortogonales |
| Orthogonal frequency-division multiplexing | Multiplexación por División de Frecuencias Ortogonales |
| Orthogonal group | Grupo ortogonal |
| Orthogonal matrix | Matriz ortogonal |
| orthographic | ortográfico |
| orthographical | perpendicular |
| orthography | ortografía |
| Orthomolecular medicine | Medicina ortomolecular |
| Orthomyxoviridae | Orthomyxoviridae |
| Orthonectida | Orthonectida |
| Orthonormality | Ortonormal |
| orthopaedic | ortopédico |
| orthopaedics | ortopedia |
| orthopaedist | ortopedista |
| orthopedic | ortopédico |
| Orthopedic surgery | Cirugía ortopédica y traumatología |
| orthopedics | ortopedia |
| orthopedist | ortopedista |
| Orthophoto | Ortofotografía |
| Orthopnoea | Ortopnea |
| Orthoptera | Orthoptera |
| orthopteran | ortópteros |
| Orthorexia nervosa | Ortorexia |
| Orthoscopic eyepiece | Ocular ortoscópico |
| Orthrus | Ortro |
| Orto Botanico di Firenze | Jardín de los Simples de Florencia |
| Orto botanico di Padova | Jardín Botánico de Padua |
| Orto botanico di Palermo | Jardín Botánico de Palermo |
| Orto botanico di Pisa | Jardín Botánico de Pisa |
| Ortobene | Ortobene |
| Ortygia | Ortigia |
| Oruchuban Ebichu | Oruchuban Ebichu |
| Oruro Department | Departamento de Oruro |
| Oruç Reis | Aruj |
| Orvieto | Orvieto |
| Orville Turnquest | Orville Alton Turnquest |
| Orville Wright | Orville Wright |
| Orvin | Orvin |
| Oryctolagus | Oryctolagus cuniculus |
| Oryol | Orël |
| Oryol Oblast | Óblast de Oryol |
| Oryx and Crake | Oryx y Crake |
| Oryza | Oryza sativa |
| Oryzomys | Oryzomys |
| Orzens | Orzens |
| Orūzgān Province | Provincia de Urūzgān |
| OS | Sistema operativo |
| Os Ancares | Comarca de Los Ancares |
| Os Blancos | Blancos |
| Os Lusíadas | Os Lusíadas |
| Os Pinos | Os Pinos |
| Osachi Hamaguchi | Hamaguchi Osachi |
| Osage Nation | Osage |
| Osaka | Osaka |
| Osaka Castle | Castillo de Osaka |
| Osaka City University | Universidad de Osaka |
| Osaka Municipal Subway | Metro de Osaka |
| Osaka Prefecture | Prefectura de Osaka |
| Osama bin Laden | Osama bin Laden |
| Osami Nagano | Osami Nagano |
| Osamu Dazai | Osamu Dazai |
| Osamu Tezuka | Osamu Tezuka |
| Osborne House | Castillo de Osborne |
| Osborne Reynolds | Osborne Reynolds |
| Osbourne Fleming | Osbourne Fleming |
| Osburga | Osburga |
| Oscan language | Osco |
| Oscar | Premios Oscar |
| Oscar Alberto Ortiz | Oscar Ortiz |
| Oscar Alfredo Gálvez | Oscar Alfredo Gálvez |
| Oscar Bonavena | Oscar Bonavena |
| Oscar Camenzind | Oscar Camenzind |
| Oscar class submarine | Premios Oscar |
| Oscar de la Hoya | Óscar de la Hoya |
| Oscar Gustave Rejlander | Oscar Gustav Rejlander |
| Oscar Gutierrez | Óscar Gutiérrez |
| Oscar Hammerstein II | Oscar Hammerstein II |
| Oscar Hernandez | Óscar Hernández |
| Oscar Hertwig | Oscar Hertwig |
| Oscar I of Sweden | Óscar I |
| Oscar II of Sweden | Óscar II |
| Oscar Luigi Scalfaro | Oscar Luigi Scalfaro |
| Oscar López Hernández | Óscar López |
| Oscar Montelius | Oscar Montelius |
| Oscar Niemeyer | Oscar Niemeyer |
| Oscar Panno | Oscar Panno |
| Oscar Peterson | Oscar Peterson |
| Oscar Robertson | Oscar Robertson |
| Oscar Ruggeri | Oscar Ruggeri |
| Oscar Schlömilch | Oskar Schlömilch |
| Oscar Serrano Rodríguez | Óscar Serrano |
| Oscar Tabárez | Oscar Washington Tabárez |
| Oscar Temaru | Oscar Temaru |
| Oscar Ustari | Oscar Ustari |
| Oscar Wilde | Oscar Wilde |
| Osceola County | Condado de Osceola |
| oscillate | oscilar |
| oscillating | vibratorio |
| Oscillating universe | Universo oscilante |
| oscillation | oscilación |
| oscillator | oscilador |
| Oscillator strength | Fuerza de oscilador |
| Oscillatoria | Oscillatoria |
| oscillatory | oscilatorio |
| Oscillatory Universe | Universo oscilante |
| Osco | Osco |
| Osculating orbit | Órbita osculatriz |
| osculation | osculación |
| Osculatory element | Elemento osculador |
| Osculum infame | Osculum infame |
| Oseberg | Barco de Oseberg |
| Oseberg ship | Barco de Oseberg |
| Osechi | Osechi |
| Osella | Osella |
| Oseltamivir | Oseltamivir |
| OSEU | Universidad Económica Estatal de Odesa |
| Osgiliath | Osgiliath |
| Oshare kei | Oshare Kei |
| Oshikoto Region | Oshikoto |
| Oshima Peninsula | Península de Oshima |
| Oshima Subprefecture | Subprefectura de Oshima |
| Oshiwambo language | Oshiwambo |
| Osho | Osho |
| Oshun | Oshun |
| OSI | OSI |
| OSI model | Modelo de interconexión de sistemas abiertos |
| osier | mimbre |
| Osijek | Osijek |
| Osijek-Baranja County | Condado de Osijek-Baranja |
| Osip Mandelstam | Osip Mandelstam |
| Osirak | Osirak |
| Osiris | Osiris |
| Osiris Shoes | Osiris |
| Oskar Kokoschka | Oskar Kokoschka |
| Oskar Lafontaine | Oskar Lafontaine |
| Oskar Morgenstern | Oskar Morgenstern |
| Oskar Panizza | Oskar Panizza |
| Oskar Schindler | Oskar Schindler |
