a person engaged, employed, or skilled in some branch of work, esp. productive or industrial work; worker.

a detective.

a secret agent; spy.

operating, or exerting force, power, or influence.

having force; being in effect or operation

laws operative in this city.

effective or efficacious.

engaged in, concerned with, or pertaining to work or productive activity.

significant; key

The operative word in that sentence is sometimes.

Medicine/Medical . concerned with, involving, or pertaining to surgical operations.

adjective

inactive , ineffective , ineffectual , inoperative , unfunctional , unworking , useless , worthless

adjective

accessible , alive , crucial , current , dynamic , effective , efficient , employable , functional , important , indicative , in force , in operation , key , live , open , operational , practicable , relevant , running , serviceable , significant , standing , usable , workable , working , operable , utilizable , functioning , going , operating , active , agent , detective , hand , in use , manipulative , spy

noun

hand , roustabout , worker , working girl , workingman , workingwoman , workman , workwoman , agent