Marked by qualities giving the power to produce an intended effect.

Producing or capable of producing an intended result or having a striking effect:
— An efficacious law.

synonyms: effective, effectual.

Roget 157: powerful, puissant; potential; capable, able; equal to, up to; cogent, valid; efficient, productive; effective, effectual, efficacious, adequate, competent; multipotent^†, plenipotent^†, omnipotent; almighty.    forcible etc. adj.. (energetic) 171; influential etc. 175; productive etc. 168.    ... show more

Roget 170: operative, efficient, efficacious, practical, effectual.    at work, on foot; acting etc. (doing) 680; in operation, in force, in action, in play, in exercise; acted upon, wrought upon.    ... show more

Roget 644: useful; of use etc. n.; serviceable, proficuous^†, good for; subservient etc. (instrumental) 631; conducive etc. (tending) 176; subsidiary etc. (helping) 707.    advantageous etc. (beneficial) 648; profitable, gainful, remunerative, worth one's salt; valuable; prolific etc. (productive) 168.    adequate; efficient, efficacious; effective, effectual; expedient etc. 646.    applicable, available, ready, handy, at hand, tangible; commodious, adaptable; of all work.    ... show more