| Otter Lake, Michigan | Otter Lake, Quebec | Otterbein, Indiana |
| Ottertail, Minnesota | Otterville, Illinois | Ottilie Wildermuth |
| Ottmar Hitzfeld | Otto | Otto Addo |
| Otto Andersson (footballer) | Otto Bardenhewer | Otto Barić |
| Otto Bühler | Otto Braun | Otto Braun (Li De) |
| Otto cycle | Otto Devrient | Otto Diels |
| Otto Erich Hartleben | Otto Ernst Remer | Otto Flake |
| Otto Fredrik Tullberg | Otto Fritz Meyerhof | Otto Gildemeister |
| Otto Grotewohl | Otto Hahn | Otto Heinrich Warburg |
| Otto Julius Bierbaum | Otto Karl Berg | Otto Kuntze |
| Otto Lilienthal | Otto Loewi | Otto Manninen |
| Otto Nerz | Otto Neurath | Otto of Freising |
| Otto Peretzl | Otto Pfister | Otto Preminger |
| Otto Pretzl | Otto Rank | Otto Rehhagel |
| Otto Schindewolf | Otto Schmidt | Otto Siffling |
| Otto Sirgo | Otto Stapf | Otto Stern |
| Otto Township, Michigan | Otto von Bismarck | Otto von Guericke |
| Otto von Kotzebue | Otto von Münchhausen | Otto Wallach |
| Otto Weddigen | Otto Wilhelm Sonder | Otto Wille Kuusinen |
| Otto, New York | Ottobiano | Ottoman architecture |
| Ottoman Aviation Squadrons | Ottoman Cyprus | Ottoman Dynasty |
| Ottoman Empire | Ottoman fleet organisation during the Greco-Turkish War (1897) | Ottoman invasion of Otranto |
| Ottoman lira | Ottoman military band | Ottoman return of Mecca 1813 |
| Ottoman ship Mahmudiye | Ottoman wars in Europe | Ottoman–German alliance |
| Ottoman–Mamluk War (1516–17) | Ottoman–Persian War (1722–27) | Ottoman–Persian War (1730–35) |
| Ottoman–Persian War (1743–46) | Ottoman–Persian War (1775–76) | Ottoman–Persian War (1821–23) |
| Ottoman–Persian Wars | Ottoman–Portuguese conflicts | Ottoman–Safavid War (1603–18) |
| Ottoman–Safavid War (1623–39) | Ottoman–Wahhabi War | Ottonian dynasty |
| Ottosen, Iowa | Ottoville, Ohio | Ottrelite |
| Ottumwa, Iowa | Otus | Otus brucei |
| Otus scops | Otv | OTV |
| Otway, Ohio | Ouachita Parish, Louisiana | Ouad Essafa |
| Ouadi Doum air raid | Ouagadougou | Ouagadougou Airport |
| Oualqadi | Ouaouizeght | Ouargla |
| Ouarzazate Airport | Ouarzazate Province | Ouday Raad |
| Oudenone | Oudjat | Oued Amlil |
| Oued Chorfa | Oued Ed-Dahab-Lagouira | Oued El Makhazine |
| Oued Fodda | Oued Irara–Krim Belkacem Airport | Oued L'Bour |
| Ouida | Ouided Kilani | Ouija |
| Ouija (2014 film) | Ouizeght | Oujé-Bougoumou, Quebec |
| Oujda | Oujda Group | Oulad Aissa |
| Oulad Ali Youssef | Oulad Ayyad | Oulad Ben Hammadi |
| Oulad Berhil | Oulad Bourima | Oulad Chrif |
| Oulad Daoud | Oulad Gnaou | Oulad Hcine |
| Oulad M'Rah | Oulad Moumna | Oulad Nouel |
| Oulad Said L'Oued | Oulad Slama | Oulad Teima |
| Oulad Yaich | Oultrejordain | Oulu, Wisconsin |
| Oum | Oum Rabia | Oumar Barro |
| Oumar Kalabane | Oumar N'Diaye (footballer born 1988) | Oumar Sissoko |
| Oumar Tchomogo | Oumou Sangaré | Oumou Sangare |
| Ounce | Ouneine | Ounnana |
| Oupa Manyisa | Our Family Wedding | Our last best chance |
| Our Last Best Chance | Our Town (1940 film) | Ouran High School Host Club |
| Ourang Medan | Ourapteryx sambucaria | Ouray, Colorado |
| Ourebia ourebi | Ouroborus cataphractus | Ourton |
| Ourtzagh | Ous Ibrahim | Ousman Jallow |
| Ousmane Bangoura | Ousmane Coulibaly | Ousmane Dabo |
| Ousmane N'Doye | Ousmane Sanou | Ousmane Viera |
| Oussama Assaidi | Oussama Darragi | Oussama Housne |
| Oussama Khatib | Oussama Mellouli | Out (magazine) |
| Out for Justice | Out in the Dark | Out of Africa (film) |
| Out of Season (short story) | Out of the Furnace | Out of the Woods (song) |
| Out of Touch | Out Run | Out Run Europa |
| Out-of-body experience | Out-of-home advertising | Outbreak |
| Outcrop | Outer ear | Outer islands of Mauritius |
| Outer space | Outer Space Treaty | Outfit7 |
| Outlast | Outlier | Outline of biotechnology |
| Outline of communication | Outline of education | Outline of human intelligence |
| Outline of manufacturing | Outline of marketing | Outline of object recognition |
| Outline of physical science | Outline of public affairs | Outline of space science |
| Outline of space technology | Outline of water | Outlive |
| OutLook | Outlook, Montana | Outlook.com |
| Output | Output device | Output elasticity |
| Output impedance | Outrage constraint | Outrage factor |
| Outreau | OutRun 2 | OutRun 2006: Coast 2 Coast |
| OutRun 2019 | OutRun Online Arcade | OutRunners |
| Outside broadcasting | Outside the Law (2010 film) | Outsource marketing |
| Outsourcing | Ouve-Wirquin | Ouya |
| Ouzinkie, Alaska | Ouzioua | OVA |
| Oval Office | Ovan Lake | Ovar |
| Ovarian artery | Ovarian branch of uterine artery | Ovarian cancer |
| Ovarian reserve | Ovarian serous cystadenoma | Ovarian vein |
| Ovary | Oven | Oven temperatures |
| Over the Garden Wall (2014 TV series) | Over the Hedge (film) | Over-the-counter drug |
| Over-the-counter substance | Overachievement | Overactive bladder |
| Overall | Overbite | Overbrook, Kansas |
| Overclocking | Overcurrent | Overdraft |
| Overdrafting | Overeating | Overeem |
| Overengineering | Overexploitation | Overgrazing |
| Overhead (engineering) | Overhead power line | Overhead projector |
| Overisel Township, Michigan | Overjet | Overland Park, Kansas |
| Overlap syndrome | Overly, North Dakota | Overpass |
| Overproduction | Overseas departments and territories of France | Overtime |
| Overtime (sports) | Overtime rate | Overton, Nebraska |
| Overweight | Overwintering | Ovibos moschatus |
| Ovid (village), New York | Ovid Township, Branch County, Michigan | Ovid Township, Clinton County, Michigan |
| Ovid, Colorado | Ovid, Michigan | Ovidiu Petre |
| Ovidiu Stanga | Ovidiu Stângă | Ovidy Karuru |
| Ovilla, Texas | Ovine rinderpest | Oviraptor. philoceratops |
| Oviraptoridae | Ovis | Ovis ammon |
