What is another word for "operative"?

Roget's Thesaurus (1911) lists these synonyms for "operative": act, acting, action, agency, bear, bring, causation, come, despair, doing, effect, effectual, efficacious, efficient, exercise, foot, force, free, function, have, home, influence, instrumentality, interaction, interworking, into, lest, maintain, maintenance, mix, modus, must, myself, office, operate, operation, perform, play, power, practical.