| ORM | orosomucoid; other regulated material; oxygen ratio monitor |
|---|---|
| ORMC | oxygen ratio monitor controller |
| ORS | olfactory reference syndrome; oral rehydration solution; oral surgery, oral surgeon; Orthopaedic Res... |
| OS | left eye [Lat. oculus sinister]; occipitosacral; occupational safety; office surgery; Omenn syndrome... |
| OSM | ovine submaxillary mucin; oxygen saturation meter |