| Ogooué River | Ogooué |
| Ogooué-Ivindo | Provincia de Ogooué-Ivindo |
| Ogooué-Lolo | Provincia de Ogooué-Lolo |
| Ogooué-Maritime | Provincia de Ogooué-Maritime |
| Ogoun | Oggun |
| ogre | ogro |
| Ogum | Oggun |
| Ogun State | Oggun |
| Ogygia | Ogigia |
| oh | ah |
| OH absorption | Absorción OH |
| OH cloud | Nube OH |
| OH emission | Emisión OH |
| OH IR star | Estrella OH infrarroja |
| OH line | Línea OH |
| OH radical | Radical OH |
| OH source | Fuente OH |
| oh well | y bueno |
| OH-absorption | Absorción OH |
| Ohangwena Region | Ohangwena |
| Ohio | Ohio |
| Ohio - Columbus | Estado de los Estados Unidos de América |
| Ohio class submarine | Clase Ohio |
| Ohio Country | Ohio Country |
| Ohio River | Río Ohio |
| Ohio Valley Wrestling | Ohio Valley Wrestling |
| Ohio Wesleyan University | Universidad Wesleyana de Ohio |
| Ohkay Owingeh Pueblo | San Juan |
| Ohlone | Ohlone |
| ohm | ohm |
| Ohm River | Ohmio |
| Ohm's law | Ley de Ohm |
| Ohrdruf | Ohrdruf |
| Ohrekreis | Ohrekreis |
| Ohrid | Ohrid |
| Ohrid municipality | Ohrid |
| Oi | OI |
| Oiartzun | Oyarzun |
| Oidium | Mildiu |
| Oier Olazábal Paredes | Oier Olazábal Paredes |
| Oignon | Allium cepa |
| Oikoumene | Ecúmene |
| oil | petróleo |
| oil and fat industry | industria de aceites y grasas |
| oil binding agent | agente astringente de petróleo |
| oil change | cambio de aceite |
| oil color | pintura al óleo |
| Oil cruet | Aceitero |
| oil disaster | catástrofe petrolera |
| oil exploration | exploración de gas natural y petróleo |
| oil extraction | extracción de petróleo |
| oil field | campo petrolífero |
| Oil flow meter | Caudalímetro |
| Oil of olives | Aceite de oliva |
| oil of turpentine | aceite de trementina |
| oil paint | pintura al óleo |
| oil painting | pintura al óleo |
| oil pan | cárter |
| oil pipeline | oleoducto |
| oil pollution | contaminación de petróleo |
| oil pollution abatement | disminución de contaminación de petróleo |
| oil production | producción de petróleo |
| Oil quality | Aceite |
| oil recovery vessel | nave de recuperación de petróleo |
| oil refinery | refinería de petróleo |
| Oil reserves | Reservas estratégicas de petróleo |
| oil residue recuperation | recuperación de residuos de petróleo |
| oil rig | equipo de perforación petrolera |
| oil slick | mancha de petróleo |
| oil spill | marea negra |
| oil tanker | petrolero |
| oil well | pozo de petróleo |
| Oil works | Acetería |
| oil-based energy | energía basada en el petróleo |
| oil-bearing | petrolífero |
| Oil-drop experiment | Experimento de la gota de aceite |
| Oil-slick | Derrame de petróleo |
| oilcan | aceitera |
| oilcloth | hule |
| oiler | engrasador |
| oiling | aceitado |
| oilskin | gabán de lona encerada |
| oilskin raincoat | gabán de lona encerada |
| oilskin suit | impermeable de hule |
| oilskins | impermeable de hule |
| oily | aceitoso |
| Oily fish | Pescado azul |
| oink | gruñir |
| ointment | pomada |
| ointment for burns | ungüento para quemaduras |
| Oireachtas | Oireachtas |
| Oise | Oise |
| Oise River | Río Oise |
| Oita Trinita | Oita Trinita |
| Ojamajo Doremi | Magical Doremi |
