Merriam-Webster Collegiate Dictionary - operative

 I. adjective  Date: 15th century  1.  a. producing an appropriate effect ; efficacious  b. most significant or essential the ~ word in a phrase  2. exerting force or influence ; operating  3.  a. having to do with physical operations (as of machines)  b. working an ~ craftsman  4. based on or consisting of an operation ~ dentistry  • ~ly adverb  • ~ness noun  II. noun  Date: circa 1810 operator: as  a. artisan, mechanic  b. a secret agent  c. private detective  d. a person who works toward achieving the objectives of a larger interest political ~s