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.(adjective)
source: webster1913
noun (n)
An efficient cause; a prime mover.(noun)
source: webster1913
adjective satellite (s)
able to accomplish a purpose; functioning effectively(adj.all)
Example: An efficient secretary.
The efficient cause of the revolution.