- obvious fingerprint
- obviously improper administrative
- OBW
- OB型星
- OB型超巨星
- OB星协
- OB星团
- OC
- OCA
- Ocagne
- OCAM
- O-carcinotron
- OCAT
- Occam's razor
- occasion
- occasional
- occasionalism
- Occasional Notes with Leisure Motions
- occasional serial
- occasional species
- Occidental Gardens and Parks
- occipital area
- occipital bone
- occipital lobe
- occipital region