Efficient

Part of speech: noun (n.)

An efficient cause; a prime mover. God . . . moveth mere natural agents as an efficient only. Hooker.

Part of speech: adjective (a.)

Causing effects; producing results; that makes the effect to be what it is; actively operative; not inactive, slack, or incapable; characterized by energetic and useful activity; as, an efficient officer, power. The efficient cause is the working cause. Wilson.

Synonyms: Effective; effectual; competent; able; capable; material; potent.