BE IN ACTION &c. adj.; operate, work; act, act upon; perform, play, support, sustain, strain, maintain, take effect, quicken, strike.
come -, bring- into -operation, - play; have play, have free play; bring to bear upon.
OPERATIVE, operant [rare], efficient, efficacious, practical, exertive, conative, effectual.
at work, on foot; acting (doing) [See Action]; in operation, in force, in action, in play, in exercise; acted upon, wrought upon.