operative

a. [ Cf.L. operativus, F. opératif. ] 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. South. [ 1913 Webster ]

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

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

n. 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 ]