- overstep the mark
- one or two
- one armed bandit
- ornamented
- oracular
- official language commission
- originating
- one who talks sweet nothings
- opression
- on trial
- opening up
- outage
- outfight
- one who awakens (through one's teachings)
- option list
- on hands
- of no value
- open door
- off the top of head
- on parade
- output statement
- output unit
- output valve
- outlet value
- organology
- okayed
- opt for
- of or pertaining to a teacher
- orienteering
- orbital
- on concession
- oesophagus
- outgoing feeder
- overreact
- onyx
- one who calls for the recovery of his due
- osteone
- oral examination
- oversee
- one's own will
- owing to
- own coding
- one who consumes liquor
- ou
- open university
- one who practices
- odontogenic zone
- organ loft
- orchestra pit
- organization of american states