ef·fi·ca·cious 
(ĕf′ĭ-kāshəs)
(ĕf′ĭ-kāshəs)adj.
Producing or capable of producing a desired effect. See Synonyms at effective.
[From Latin efficāx, efficāc-, from efficere, to effect; see EFFECT.]
ef′fi·cacious·ly adv.
ef′fi·cacious·ness n.