Nouns

(n)secret agent, intelligence officer, intelligence agent, operativea person secretly employed in espionage for a government
(n)private detective, PI, private eye, private investigator, operative, shamus, sherlocksomeone who can be employed as a detective to collect information and assist in criminal investigations

Adjectives

(a)operativebeing in force or having or exerting force“operative regulations”, “the major tendencies operative in the American political system”
(a)surgical, operativerelating to or requiring or amenable to treatment by surgery especially as opposed to medicine“a surgical appendix”, “a surgical procedure”, “operative dentistry”
(s)operativeeffective; producing a desired effect“the operative word”
(s)running, operative, functional, working(of e.g. a machine) performing or capable of performing“in running (or working) order”, “a functional set of brakes”