(n) grand opera
(n) comic opera
(n) space opera
(n) thiopental
(adj-na) operational
(n) operations
(n) operating
(n) operant conditioning
(n) operant conditioning
(n) (comp) cable operator
(n) (comp) system operator (sysop)
(n) (comp) local operator
(n) buying operation
(n) selling operation
(n) (comp) operation code
op-code
(n) (comp) operating environment
(n) (comp) interoperability
(n) operation center
operation centre
(n) operation twist
(n) operations research
(n) cooperative system
(n) interoperability
(n) operations research
OR
(n) (comp) Operations manuals
(n) (comp) operating-system
OS
(n) operating margin
(n) (comp) operating-system
OS
(n) smoothing operation
(n) (comp) Regional Bell Operating Company (USA)
RBOC
(n) open market operation