| onormal | deviant |
| onormalt | abnormally |
| Onotoa | Onotoa |
| Ons Hémécht | Ons Hémécht |
| onsdag | Wednesday |
| Onsernone | Onsernone |
| Onsjö härad | Onsjö Hundred |
| ont | harm |
| ont i halsen | sore throat |
| ont i huvudet | have a headache |
| ont om | short of |
| ont skall med ont fördrivas | fight fire with fire |
| Ontario | Ontario |
| Ontario Hockey League | Ontario Hockey League |
| Ontariosjön | Lake Ontario |
| ontogeni | ontogenesis |
| ontologi | ontology |
| Ontologiska gudsbeviset | Ontological argument |
| OntoMeeting | OntoMeeting |
| Ontronik Khachaturian | Ontronik Khachaturian |
| ONUC | United Nations Operation in the Congo |
| onumrerad | unnumbered |
| onykter | drunk |
