| Orthodoxie | Orthodoxy |
| Orthorexie | orthorexia |
| orthodox | orthodox |
| Neuorthodoxie | orthodoxy |
| Orthoepie | orthoepy |
| Orthopädie | orthopaedics orthoorthopedicsaedics |
| Hochorthodoxie | orthodoxy |
| Orthogon | rectangle |
| unorthodox | licentious |
| Orthofoto | orthophoto |
| Orthografie | orthography spelling |
| Orthopäde | orthopedist orthopaedist orthopaedic specialist orthopedic specialist orthopedic surgeon |
| Orthopädin | orthopaedic specialist orthopaedist orthopedic specialist orthopedist |
| orthogonal | orthogonal |
| Arthrologie | arthrology |
| Anthologie | anthology |
| Ethologie | ethology behavioural research |
| Mythologie | mythology |
| Ornithologie | ornithology |
| Pathologie | patology pathology |