| om | ohm |
| Om mani padme hum | Om mani padme hum |
| Omacnica prosowianka | European Corn Borer |
| Omacnica spichrzanka | Indian meal moth |
| Omacnicowate | Pyralidae |
| Omaha | Omaha |
| Omaha Ak-Sar-Ben Knights | Omaha Ak-Sar-Ben Knights |
| omal | almost |
| Oman | Oman |
| Omar | Umar |
| Omar al-Baszir | Omar al-Bashir |
| Omar Andrés Narváez | Omar Andrés Narváez |
| Omar Bongo | Omar Bongo |
| Omar Bradley | Omar Bradley |
| Omar Chajjam | Omar Khayyám |
| Omar Hashim Epps | Omar Epps |
| Omar Ibn al-Farid | Ibn al-Farid |
| Omar Karami | Omar Karami |
| Omar Mukhtar | Omar Mukhtar |
| Omar Pène | Omar Pène |
| Omar Sharif | Omar Sharif |
| Omar Sívori | Omar Sívori |
| Omari Tetradze | Omari Tetradze |
| Omarlicowate | Silphidae |
| Omatnikowate | Tangle web spider |
| omawiać | broach |
| ombudsman | ombudsman |
| Omdurman | Omdurman |
| omega | omega |
| Omega Centauri | Omega Centauri |
| OmegaWiki | WiktionaryZ |
| Omegna | Omegna |
| omen | omen |
| Omerta | Omertà |
| Ometecuhtli | Ometecuhtli |
| Ometeotl | Ometeotl |
| Omfacyt | Omphacite |
| Omfale | Omphale |
| Omieg | Doronicum |
| omijać | bypass |
| omikron | omicron |
| Omikron Andromedae | Omicron Andromedae |
| omlet | omelette |
| Omloop Het Volk | Omloop Het Volk |
| omnibus | omnibus |
| omnipotencja | omnipotence |
| Omnitrix | List of Omnitrix aliens |
| Omo | Omo River |
| omocznia | allantois |
| Omoforion | Omophorion |
| Omomiłkowate | Soldier beetle |
| OMON | OMON |
| Omonia Nikozja | AC Omonia |
| omowy | ohmic |
| Omołon | Omolon River |
| OMR | Optical mark recognition |
| Omri | Omri |
| Omri Szaron | Omri Sharon |
| Omsk | Omsk |
| Omskavia | Omskavia |
| Omurtag | Omurtag of Bulgaria |
| omułek | blue mussel |
| OMV | OMV |
| on | he |
| On an Island | On an Island |
| On the Night | On the Night |
| On Through The Night | On Through the Night |
| ON-Line System | NLS |
| ona | she |
| Ona mnie nienawidzi | She Hate Me |
| onager | onager |
| Onan | Onan |
| Onani | Onani |
| onanizm | masturbation |
| Once in a LIVEtime | Once in a LIVEtime |
| Oncilla | Oncilla |
| Ondansetron | Ondansetron |
| Ondava | Ondava |
| Ondo | Ondo State |
| Ondol | Ondol |
| Ondrašová | Ondrašová |
| Ondyna | Ondine |
| Ondyny | Ondine |
| one | they |
| One Canada Square | One Canada Square |
| One Life To Live | One Life to Live |
| One Night Stand | WWE One Night Stand |
| One Piece | One Piece |
| One Step Closer | One Step Closer |
| Oneg Szabat | Oyneg Shabbos |
| Onega | Lake Onega |
| OneRepublic | OneRepublic |
| Oneworld | Oneworld |
| Onex | Onex |
| Oneşti | Oneşti |
| oni | they |
| Oni żyją | They Live |
| oniemiały | speechless |
| Onikan Stadium | Onikan Stadium |
| Onikszty | Anykščiai |
| onkologia | oncology |
| Online analytical processing | Online analytical processing |
| Onmyoza | Onmyo-Za |
| Onnens | Onnens |
| ono | it |
| onomastyka | onomastics |
| onomatopeja | onomatopoeia |
| Onon | Onon River |
| ONP | RPN |
| Onsen | Onsen |
| Onsernone | Onsernone |
| Ontario | Ontario |
| Ontario Hockey League | Ontario Hockey League |
| ontogeneza | ontogenesis |
| ontologia | ontology |
| ontologiczny | ontological |
| Ontronik Khachaturian | Ontronik Khachaturian |
| ONUB | United Nations Operation in Burundi |
| onuca | footwrap |
| Onufry Kopczyński | Onufry Kopczynski |
| ONZ | United Nations |
| OODA | OODA Loop |
| Oogamia | Oogamy |
| Oolity | Roestone |
| Oomoto | Oomoto |
| Oorlans | Oorlans |
| Oosterpark Stadion | Oosterpark Stadion |
| OOŚ | EIA |
| Opabinia | Opabinia |
| OPAC | OPAC |
| opactwo | abbey |
| Opactwo Clairvaux | Clairvaux Abbey |
| Opactwo cystersów w Sulejowie | Cistercians Abbey in Sulejów |
| Opactwo Cîteaux | Cîteaux Abbey |
| Opactwo Dunfermline | Dunfermline Abbey |
| Opactwo Fontenay | Abbey of Fontenay |
| Opactwo Hollyrood | Holyrood Abbey |
| Opactwo i klasztor Altenmünster w Lorsch | Lorsch Abbey |
| Opactwo Morimond | Morimond Abbey |
| Opactwo Northanger | Northanger Abbey |
| Opactwo Saint-Wandrille | Fontenelle Abbey |
| Opactwo Thelemy | Abbey of Thelema |
| Opactwo w Aurillac | Aurillac Abbey |
| Opactwo w Cluny | Cluny Abbey |
| Opactwo w Gigny | Gigny Abbey |
| Opactwo Westminsterskie | Westminster Abbey |
| Opad atmosferyczny | Precipitation |
| opad chemiczny | chemical fallout |
| opad kwaśnego deszczu | acid deposition |
| opad pyłu | fallout |
| opad zanieczyszczeń | pollutant deposition |
| opad zanieczyszczeń z atmosfery | atmospheric fallout |
| opady atmosferyczne | precipitation |
| opakowanie | package |
| opakowanie dodatkowe | additional packaging |
| opal | opal |
