A participant in an operation.
An employee or other worker with some particular function or skill.
A spy, secret agent, or detective.
Functional, in working order.
Effectual or important.
Having the power of acting; hence, exerting force, physical or moral; active in the production of effects.
Producing the appropriate or designed effect; efficacious.
Based upon, or consisting of, a surgical operation or operations.
A procedure in which one or more incisions are made into the body in order to repair damage or remove diseased tissue; an operation.