| ognitempo | all-weather |
| ognora | forever |
| ognun per sé | every man for himself |
| ognuno | all |
| ognuno di | each one of |
| Ogoni | Ogoni people |
| Ogooué | Ogooué River |
| Ogooué-Ivindo | Ogooué-Ivindo |
| Ogooué-Lolo | Ogooué-Lolo |
| Ogooué-Maritime | Ogooué-Maritime |
| Ogre | Ogre District |
| Ogun | Ogoun |
| oh | oh |
| Oh Holy Night | O Holy Night |
| Ohangwena | Ohangwena Region |
| ohi | ouch |
| Ohio | Ohio |
| Ohio Valley Wrestling | Ohio Valley Wrestling |
| Ohlenrode | Ohlenrode |
| Ohlsbach | Ohlsbach |
| Ohlstadt | Ohlstadt |
| ohm | ohm |
| Ohmden | Ohmden |
| Ohmdenosaurus liasicus | Ohmdenosaurus |
| Ohmstal | Ohmstal |
| Ohrdruf | Ohrdruf |
| Ohrenbach | Ohrenbach |
| Ohře | Ohře |
| OI | Oi |
| Oiapoche | Oiapoque |
| Oiartzun | Oiartzun |
| Oil and Natural Gas Corporation | Oil and Natural Gas Corporation |
| Oil-for-food | Oil-for-Food Programme |
| Oineo | Oeneus |
| Oinochoe | Oenochoe |
| Oinofyta | Oinofyta |
| Oinousses | Oinousses |
| Oireachtas | Oireachtas |
| Oisc del Kent | Oisc of Kent |
| Oise | Oise |
| Oita | Oita |
| OJ | OJ |
| Ojamajo Doremi | Ojamajo Doremi |
| OJI | Oji |
| Ojibway | Ojibwa |
| Ojmjakon | Oymyakon |
| Ojén | Ojen |
| Ok Go | OK Go |
| Oka | Oka River |
| okapi | okapi |
| Okapia johnstoni | Okapi |
| Okavango | Okavango River |
| okay | all right |
| OKB | OKB |
| Okhrana | Okhranka |
| Oki | Oki Province |
| Okinawa | Okinawa Island |
| Oklahoma | Oklahoma |
| Oklahoma City | Oklahoma City |
| Okondo | Okondo |
| Okonomiyaki | Okonomiyaki |
| Oksana Bajul | Oksana Baiul |
| Oktoberfest | Oktoberfest |
| Okussi-Ambeno | Oecussi-Ambeno |
| OL | OL |
| Ola Hakansson | Ola Håkansson |
| Olaberria | Olaberria |
| Olaf I di Danimarca | Olaf I of Denmark |
| Olaf I di Norvegia | Olaf I of Norway |
| Olaf IV di Norvegia | Olav IV of Norway |
| Olaf Kyrre | Olaf III of Norway |
| Olaf Kölzig | Olaf Kölzig |
| Olaf Stapledon | Olaf Stapledon |
| Olaibar | Oláibar |
| Olanda | Holland |
| Olanda Meridionale | South Holland |
| Olanda Settentrionale | North Holland |
| olandese | Dutchman |
| olandese volante | Flying Dutchman |
| olandesi | Dutch |
| Olanesti | Olanesti |
| Olanzapina | Olanzapine |
| Olao Magno | Olaus Magnus |
| OLAP | Online analytical processing |
| Olargues | Olargues |
| Olaus Rudbeck | Olaus Rudbeck |
| Olaus Rudbeck il Giovane | Olof Rudbeck the Younger |
| Olav II di Norvegia | Olaf II of Norway |
| Olav V di Norvegia | Olav V of Norway |
| Olavinlinna | Olavinlinna |
| Olbendorf | Olbendorf |
| Olbernhau | Olbernhau |
| Olbia | Olbia |
| Olching | Olching |
| Old Boy | Oldboy |
| Old English | Old English |
| Old Faithful | Old Faithful Geyser |
| Old fashioned glass | Old fashioned glass |
| Old Firm | Old Firm |
| Old Friends from Young Years | Old Friends from Young Years |
| Old Lyme | Old Lyme |
| Old Saybrook | Old Saybrook |
| Old school hip hop | Old school hip hop |
| Old Trafford | Old Trafford |
| Oldenburg | Oldenburg |
| Oldham | Oldham |
| Oldman | Oldman River |
| Ole Einar Bjørndalen | Ole Einar Bjørndalen |
| Ole Gunnar Solskjær | Ole Gunnar Solskjær |
| Ole Rømer | Ole Rømer |
| Ole von Beust | Ole von Beust |
| Olea europaea | Olive |
| Oleaceae | Oleaceae |
| oleandro | oleander |
