| Order of the British Empire | Order of the British Empire |
| Ordet | Ordet |
| ordforråd | vocabulary |
| ordinær | vulgar |
| ordklasse | part of speech |
| ordliste | glossary |
| ordning | order |
| Ordo Templi Orientis | Ordo Templi Orientis |
| Ordovicium | Ordovician |
| ordsprog | proverb |
| Ordsprogenes Bog | Book of Proverbs |
| Oregon | Oregon |
| Orestes | Orestes |
| Orfeus | Orpheus |
| Orfeus og Eurydike | Orfeo ed Euridice |
| organ | organ |
| Organel | Organelle |
| organisation | organisation |
| Organisationen af Amerikanske Stater | Organization of American States |
| organisationers juridiske form | legal form of organisations |
| Organisationsteori | Organizational studies |
| Organisere | Map |
| organisk affald | organic waste |
| Organisk forbindelse | Organic compound |
| organisk forurenende stof | organic pollutant |
| organisk forurening | organic pollution |
| organisk fosforforbindelse | organophosphorous compound |
| organisk halogenforbindelse | organohalogen compound |
| organisk kemi | organic chemistry |
| organisk klorforbindelse | organochlorine compound |
| organisk kulstof | organic carbon |
| organisk kvælstofforbindelse | organonitrogen compound |
| organisk metalforbindelse | organometallic compound |
| organisk nitrogen | organic nitrogen |
| organisk opløsningsmiddel | organic solvent |
| organisk oxygenforbindelse | organooxygen compound |
| organisk stof | organic matter |
| organisk svovlforbindelse | organosulphur compound |
| organiske stoffer | organic substance |
| organisme | organism |
| organismer | organism |
| Organization of the Islamic Conference | Organization of the Islamic Conference |
| organoleptisk egenskab | organoleptic property |
| orgasme | orgasm |
| orgel | organ |
| Orgelpibe | Organ |
| Orhan Pamuk | Orhan Pamuk |
| Oriana Fallaci | Oriana Fallaci |
| Orientalsk | Oriental |
| Orientalsk despoti | Hydraulic despotism |
| Orientekspressen | Orient Express |
| Orienten | Orient |
| orienteret graf | directed graph |
| Origami | Origami |
| Origenes | Origen |
| original | genuine |
| Original Six | Original Six |
| Orinoco | Orinoco |
| Orio al Serio International Airport | Orio al Serio Airport |
| Orion | Orion |
| Oriontågen | Orion Nebula |
| Orissa | Orissa |
| orkan | hurricane |
| Orkan Katrina | Hurricane Katrina |
| Orkanen Isabel | Hurricane Isabel |
| Orkdal | Orkdal |
| orkester | orchestra |
| orkide | orchid |
| Orkla | Orkla Group |
| Orkneyøerne | Orkneys |
| Orkut | Orkut |
| Orlando | Orlando |
| Orlando Bloom | Orlando Bloom |
| Orlando di Lasso | Orlande de Lassus |
| Orléans | Orleans |
| orm | worm |
| Ormehul | Wormhole |
| Ormen hin Lange | Ormen Lange |
| Ormen Lange | Ormen Lange |
| Ormtjernkampen nationalpark | Ormtjernkampen National Park |
| Ormurin langi | Ormurin Langi |
| Ornament | Robes of office |
| orne | boar |
| Ornithomimus | Ornithomimus |
| ornitologi | ornithology |
| orografi | orography |
| Orsa | Orsha |
| Orson Scott Card | Orson Scott Card |
| Orson Welles | Orson Welles |
| Orthoptera | orthopteran |
| Orthosie | Orthosie |
| Ortodoks jødedom | Orthodox Judaism |
| Ortodokse kirker | Eastern Orthodox Church |
| Ortogonal matrix | Orthogonal matrix |
| Ortografi | Orthography |
| Ortonormal | Orthonormality |
| Ortonormal basis | Orthonormal basis |
| Ortopædkirurgi | Orthopedic surgery |
| Ortoreksi | Orthorexia nervosa |
| Orvieto | Orvieto |
| Orville Wright | Orville Wright |
| Orwellsk | Orwellian |
| Os i Hordaland | Bone |
| Osaka | Osaka |
| Osama bin Laden | Osama bin Laden |
| Osamu Tezuka | Osamu Tezuka |
| Osby kommun | Osby Municipality |
| Oscar | Oscar |
| Oscar Bernadotte | Count Oscar Bernadotte of Wisborg |
| Oscar Camenzind | Oscar Camenzind |
| Oscar for bedste animationsfilm | Academy Award for Best Animated Feature |
| Oscar for bedste dokumentar | Academy Award for Documentary Feature |
| Oscar for bedste film | Academy Award for Best Picture |
| Oscar for bedste filmatisering | Academy Award for Writing Adapted Screenplay |
| Oscar for bedste fotografering | Academy Award for Best Cinematography |
| Oscar for bedste instruktør | Academy Award for Best Director |
| Oscar for bedste kortfilm | Academy Award for Live Action Short Film |
| Oscar for bedste kvindelige birolle | Academy Award for Best Supporting Actress |
| Oscar for bedste kvindelige hovedrolle | Academy Award for Best Actress |
| Oscar for bedste mandlige birolle | Academy Award for Best Supporting Actor |
| Oscar for bedste mandlige hovedrolle | Academy Award for Best Actor |
| Oscar for bedste musik | Academy Award for Original Music Score |
| Oscar for bedste originale manuskript | Academy Award for Writing Original Screenplay |
| Oscar for bedste udenlandske film | Academy Award for Best Foreign Language Film |
| Oscar Niemeyer | Oscar Niemeyer |
| Oscar Peterson | Oscar Peterson |
| Oscar Wendt | Oscar Wendt |
| Oscar Wilde | Oscar Wilde |
| Oscarsborg | Oscarsborg Fortress |
| Oscaruddelingen | Academy Award |
| OSCE | Organization for Security and Co-operation in Europe |
| Oscillator | Oscillation |
| Osebergskibet | Oseberg ship |
| Osen | Osen |
| Osgiliath | Osgiliath |
| OSI-model | OSI model |
| Osijek | Osijek |
| Osip Mandelstam | Osip Mandelstam |
| Osiris | Osiris |
| Oskar Kokoschka | Oskar Kokoschka |
| Oskar Lafontaine | Oskar Lafontaine |
| Oskar Schindler | Oskar Schindler |
| Oskarshamn kernekraftværk | OKG |
| Oslo | Oslo |
| Oslo Filharmoniske Orkester | Oslo Philharmonic |
| Oslofjorden | Oslofjord |
| Osmanniske Rige | Ottoman Empire |
| Osmanthus | Osmanthus |
| osmium | osmium |
| osmose | osmosis |
| Osnabrück | Osnabrück |
| Ossetere | Ossetians |
| Ossetisk | Ossetic language |
| Osso buco | Ossobuco |
| ost | cheese |
| Ostarrîchi | Ostarrîchi |
| Ostbevern | Ostbevern |
| ostehøvl | cheese slicer |
| ostekage | cheesecake |
| Osteoporose | Osteoporosis |
| Osterøy | Osterøy |
| Ostindien | East Indies |
| Ostindisk Kompagni | Danish East India Company |
| Ostrava | Ostrava |
| Ostrogoterne | Ostrogoths |
| Ostrów Wielkopolski | Ostrów Wielkopolski |
| Osvaldo Cavandoli | Osvaldo Cavandoli |
| Osvaldo Golijov | Osvaldo Golijov |
| Oswald Mosley | Oswald Mosley |
| Otello | Otello |
| Othello | Reversi |
| Otho | Otho |
| Otis | Otis Elevator Company |
| Oto-rhino-laryngologi | Ear nose and throat |
| Otra | Otra |
| Otrantostrædet | Strait of Otranto |
| Ottakring | Ottakring |
| Ottavio Bottecchia | Ottavio Bottecchia |
| Ottawa | Ottawa |
| Ottawa Senators | Ottawa Senators |
| otte | eight |
| Ottearmet blæksprutte | Octopus |
| ottende | eighth |
| otteogfirs | eighty-eight |
| otteogfyrre | forty-eight |
| otteoghalvtreds | fifty-eight |
| otteogtredive | thirty-eight |
| otteogtredve | thirty-eight |
| otteogtres | sixty-eight |
| otteogtyve | twenty-eight |
| otter | eight |
| Otterup Kommune | Otterup municipality |
| Ottetalsknob | Figure-of-eight knot |
| Otto | Otto Mann |
| Otto af Freising | Otto of Freising |
| Otto den Store | Otto I |
| Otto Hahn | Otto Hahn |
| Otto Jespersen | Otto Jespersen |
| Otto Klemperer | Otto Klemperer |
| Otto Lilienthal | Otto Lilienthal |
| Otto Nicolai | Carl Otto Nicolai |
| Otto Robert Frisch | Otto Robert Frisch |
| Otto Skorzeny | Otto Skorzeny |
| Otto von Bismarck | Otto von Bismarck |
| Otto von Guericke | Otto von Guericke |
| Ottomotor | Spark-ignition |
| Ottorino Respighi | Ottorino Respighi |
| Ouagadougou | Ouagadougou |
| Oudenaarde | Oudenaarde |
| Oulu | Oulu |
| Oulus len | Oulu Province |
| Outeniqua Choo Tjoe | Outeniqua Choo Tjoe |
| Outland | Draenor |
| Outremer | Outremer |
| Ovamboland | Ovamboland |
| ovarium | ovary |
| Ove Høegh-Guldberg | Ove Høegh-Guldberg |
| Ove Sprogøe | Ove Sprogøe |
| oven vande | above water |
| Over hækken | Over the Hedge |
| over skyerne er himlen altid blå | every cloud has a silver lining |
| Over The Hills And Far Away | Over the Hills and Far Away |
| over- | uber- |
| Overall | Overalls |
| overalt | everywhere |
| overbefiskning | overfishing |
| overbefolkning | overpopulation |
