ogress - Ouagadougou
- osculant
- oscular
- osculate
- osculation
- OSD Office of the Secretary of Defense
- OSDIT Office of Software Development and Information Technology
- osier
- osier-bed
- Osiris
- Oslo
- osmium
- Osmond
- Osmond, Osmund
- osmose
- osmosis
- osmotic
- Osmund
- OSRD Office of Scientific Research and Development
- OSS Office of Strategic Services
- osseous