| 1 | English | optimistic | Expecting the best in all possible ways; Allowing... |
| 2 | English | Optimist | A small centre-board sailing dinghy designed to... |
| 3 | French | optimiste | optimist; optimistic |
| 4 | French | optimisme | optimism |
| 5 | Latin | optimus | best; very good |
| 6 | Latin | Ops | earth goddess, fertility deity |
| 7 | Latin | oscen | any bird by whose song cries augurs divined... |
| 8 | Latin | opscen | — |
| 9 | Latin | ob- | towards; against |
| 10 | Latin | obolus | obolus |
| 11 | Ancient Greek | ὀβολός | obol, obolus, used at Athens as both a weight and... |
| 12 | Ancient Greek | ὀβελός | a spit, rod; a horizontal line |
| 13 | Ancient Greek | βέλος | missile, arrow, dart; weapon; something quickly... |
| 14 | Proto-Indo-European | gʷélHos | — |
| 15 | Proto-Indo-European | gʷelH- | to throw, reach, pierce; to hit by throwing |