1.  operative(n = noun.person) intelligence agent, intelligence officer, secret agent - a person secretly employed in espionage for a government;
is a kind of agent
has particulars: agent-in-place, agent provocateur, provocateur, bridge agent, case officer, codetalker, windtalker, foot, noc, spy, undercover agent, walk-in

2.  operative(n = noun.person) pi, private detective, private eye, private investigator, shamus, sherlock - someone who can be employed as a detective to collect information;
is a kind of detective
has particulars: hotel detective, house detective, house dick, inquiry agent, store detective

1.  operative(a = adj.all) - being in force or having or exerting force; "operative regulations"; "the major tendencies operative in the American political system"
Antonym: inoperative

2.  operative(a = adj.all) surgical - relating to or requiring or amenable to treatment by surgery especially as opposed to medicine; "a surgical appendix"; "a surgical procedure"; "operative dentistry"
Derived forms verb operate₇, noun operation₆

3.  operative(s = adj.all) - effective; producing a desired effect; "the operative word"

4.  operative(s = adj.all) functional, running, working - (of e.g. a machine) performing or capable of performing; "in running (or working) order"; "a functional set of brakes"
Derived forms verb operate₃, verb operate₂

1.  Having the power of acting; hence, exerting force, physical or moral; active in the production of effects; as, an operative motive; operative laws. [1913 Webster]
"It holds in all operative principles." [1913 Webster]

2.  Producing the appropriate or designed effect; efficacious; effective; as, an operative dose, rule, or penalty. [1913 Webster]

3.  Based upon, or consisting of, an operation or operations; as, operative surgery. [1913 Webster]

1.  A skilled worker; an artisan; esp., one who operates a machine in a mill or manufactory. [1913 Webster]

2.  One who acts as an agent of another, especially a detective or spy. [PJC]

operative, adj. & n.
--adj.
1 in operation; having effect.
2 having the principal relevance ('may' is the operative word).
3 of or by surgery.
4 Law expressing an intent to perform a transaction.
--n.
1 a worker, esp. a skilled one.
2 US a private detective.

Derivative:
operatively adv. operativeness n.

Etymology:
LL operativus f. L (as OPERATE)

N  doer, actor, agent, performer, perpetrator, operator, executor, executrix, practitioner, worker, stager, bee, ant, working bee, termite, white ant, laboring oar, servant of all work, factotum, workman, artisan, craftsman, handicraftsman, mechanic, operative, working man, laboring man, demiurgus, hewers of wood and drawers of water, laborer, navvy, hand, man, day laborer, journeyman, charwoman, hack, mere tool, beast of burden, drudge, fag, lumper, roustabout, maker, artificer, artist, wright, manufacturer, architect, builder, mason, bricklayer, smith, forger, Vulcan, carpenter, ganger, platelayer, blacksmith, locksmith, sailmaker, wheelwright, machinist, mechanician, engineer, sempstress, semstress, seamstress, needlewoman, workwoman, tailor, cordwainer, minister, servant, representative, coworker, party to, participator in, particeps criminis, dramatis personae, personnel, quorum pars magna fui, faber est quisque fortunae suae.

N  agency, operation, force, working, strain, function, office, maintenance, exercise, work, swing, play, interworking, interaction, procurement, causation, instrumentality, influence, action, modus operandi, quickening power, maintaining power, sustaining power, home stroke, operative, efficient, efficacious, practical, effectual, at work, on foot, acting, in operation, in force, in action, in play, in exercise, acted upon, wrought upon, by the agency of through, by means of, I myself must mix with action lest I wither by des.

operative field