- oriental cholangiohepatitis
- off flavour
- one who is meticulous in preserving (one's) self_dignity
- organ of speech
- official receiver
- one's foot
- one member
- oneirology
- out of tune
- os trigonum
- ordinarily
- outstation
- on the pattern of
- off centred
- one of a class of books defining various classifications of heroes
- orchotomy
- openhandedness
- orthoscopy
- out of keeping
- outlawed
- offset stacker
- oratorical
- old maid flower
- or so
- of the order of
- overdrawn
- osteochondritis deformans juvenilis
- ophthalmic optician
- opera glasses
- office of the united nations security coordinator
- organogel
- orchestral
- ostensibly
- olefin
- off the bat
- of or pertaining to the evening
- one of these days
- old world monkey
- one for the road
- on the way
- object definition
- osteopenia
- overdo it
- overdo things
- otis i.q.
- otolith organ
- oat_cell carcinoma
- of peaceful disposition
- olive branch
- outlawry