- ottoman dynasty
- ottoman turk
- of inadequate pervasion or extent
- out of practice
- ostomy product
- orchestra
- outdoor patient
- outpatients department (opd)
- opaque
- open and shut
- of or pertaining to war
- one of the nine rasas in poetry—the sentiment of abhorrence or disgust
- old master painting
- one who speaks ill of others
- of immoral conduct
- one who speaks ill (of somebody)
- operating surgeon
- optimize
- optimise
- one who believes in the doctrine of
- opportunistic infection
- opportunistic pathogen
- opportunist saprophyte
- own flesh and blood
- order of official precedence
- outworn
- onychogenic
- owlet
- owl
- ogress
- owe
- of auspicious aspect
- opposition leader
- office or function of an agent
- operated
- owe one
- oligarchy
- of ill_luck
- operator console
- operator control language
- operator control panel
- operator command
- orthopaedic
- orthopedics
- orthopaedics
- otoscopy
- on every hand
- one to one
- one who sits in judgment
- one whose chastity has been violated