OA
osteoarthritis
OBGYN
obstetrics and gynecology
OD
overdose or oculus dexter, right eye
OE
otitis externa
OG tube
orogastric tube
OM
otitis media
Onc
oncology
OP
oropharynx
OR
operating room
ORIF
open reduction with internal fixation
Ortho
orthopedic surgery
OS
oculus sinister, left eye
OSHA
occupational health and safety administration
OTC
over the counter drug
p
post, after