The Collaborative International Dictionary of English v.0.48:

Effector \Ef*fect"or\, n. [L.]
   An effecter. --Derham.
   [1913 Webster]

WordNet (r) 3.0 (2006):

effector
    n 1: one who brings about a result or event; one who
         accomplishes a purpose [syn: effecter, effector]
    2: a nerve fiber that terminates on a muscle or gland and
       stimulates contraction or secretion
    3: an organ (a gland or muscle) that becomes active in response
       to nerve impulses [ant: receptor, sense organ, sensory
       receptor]