Definitions of operative:

• noun:   a person secretly employed in espionage for a government
• noun:   someone who can be employed as a detective to collect information
• adjective:   effective; producing a desired effect

  Example: "The operative word"

• adjective:   of or relating to a surgical operation

  Example: "Operative surgery"

• adjective:   being in force or having or exerting force

  Example: "Operative regulations"

• adjective:   (of e.g. a machine) performing or capable of performing
• adjective:   relating to or requiring or amenable to treatment by surgery especially as opposed to medicine

  Example: "Operative dentistry"