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.
An employee or other worker with some particular function or skill.
A spy, secret agent, or detective.
A participant in an operation.
A theoretical unit of measure of utility, for indicating a supposed quantity of satisfaction derived from an economic transaction.