| Oktonion | octonion |
| Oktogon | octagon |
| Doktorin | Doctor |
| Oktagon | octagon |
| Oktillion | octillion quindecillion |
| Ökoton | ecotone |
| Oxytonon | oxytone |
| Aktion | action operation promotion campaign |
| Option | option |
| Oktant | Octans |
| Doktrin | doctrine |
| Oktober | October |
| Oktole | octuplet |
| Oktopus | octopus |
| Lektorin | lecturer |
| Rektorin | headmistress |
| Tektonik | tectonics |
| Antonius | Antonius |
| Bretonin | Breton |
| Edmonton | Edmonton |