| One-Two-GO Airlines | One-Two-Go Airlines |
| Onega | Onega |
| Onegai Teacher | Onegai teacher |
| Onegai Twins | Onegai twins |
| Oneglia | Oneille |
| Oneida | Oneida |
| Oneiroi | Oneiroi |
| Onel de Guzmán | I love you |
| Oneonta | Oneonta |
| onere | épreuve |
| onere della prova | charge de la preuve |
| oneroso | pénible |
| onestamente | honnêtement |
| Onesti | Onesti |
| onesto | pur |
| onestà | candeur |
| Oneworld | Oneworld |
| Onex | Onex |
| Onfale | Omphale |
| Ongarese | Hongrois |
| onice | onyx |
| onicofagia | habitude de se ronger les ongles |
| onisco | cloporte |
| Online Certificate Status Protocol | Protocole de vérification en ligne de certificat |
| Onnens | Onnens |
| onnipotente | omnipotent |
| onnipotenza | omnipotence |
| onnipresente | doué d'ubiquité |
| onnipresenza | omniprésence |
| onnisciente | omniscient |
| onniscienza | omniscience |
| onnivoro | omnivore |
| Onofre Marimon | Onofre Marimón |
| Onomastica | Onomastique |
| Onomastica araba | Nom arabe |
| Onomasticoonomastico | Fête |
| onomatopea | onomatopée |
| Onomichi | Onomichi |
| Ononis spinosa | Bugrane épineuse |
| onorabile | honorable |
| onorare | toucher |
| onorario | honorifique |
| Onorato III di Monaco | Honoré III de Monaco |
| Onorato IV di Monaco | Honoré IV de Monaco |
| Onorato V di Monaco | Honoré V de Monaco |
| onore | honneur |
| onorevole | député |
| onorificenza | distinction |
| onorifico | honorifique |
| Onorio | Flavius Honorius |
| ONS | Once |
| Ons Heemecht | Ons Heemecht |
| Onsen | Onsen |
| Onsernone | Onsernone |
| Onslaught | Onslaught |
| onta | déshonneur |
| ontano | aulne |
| Ontario | Ontario |
| Ontelaunee Township | Ontelaunee Township |
| Ontinyent | Ontinyent |
| ontogenesi | ontogenèse |
| ontologia | ontologie |
| OntoMeeting | OntoMeeting |
| ONU | ONU |
