| OI | obturator internus; occasional insomnia; opportunistic infection; opsonic index; orgasmic impairment... |
|---|---|
| OID | optimal immunomodulating dose; Organism Identification Number; oxygen insufflation device |
| OPP | osmotic pressure of plasma; oxygen partial pressure |
| 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... |