(n) orphan drug
(n) oven toaster
toaster oven
(n) opening game
(n) open ticket
(n) open account
(n) open campus
(n) open shop system (employment of both unionists and non-unionists)
(n) open market
(n) oral approach
(n) (comp) all-in-one Personal Computer
(n) all or nothing
(n) all-star game
(adj-na) alternative
(n) Old Economy
(n) oil finish
(n) (uk) Japanese giant salamander (Andrias japonicus)
(n) (uk) scarab beetle
sacred scarab (Scarabaeus sacer)
(n) (uk) razorbill (Alca torda)
(n) oxyhemoglobin
(n) oxonium ion
(n) occidentalism
(n) osteoporosis
(n) (comp) Ostwald color system
(n) opioid peptide
(n) opinion leader
(P)
(n) official game
(n) official handicap (golf)
(n) office amenity
(n) off-site centre (center)
(n) offside trap