WordNet (r) 3.0 (2006):

parasympathetic nervous system
    n 1: originates in the brain stem and lower part of the spinal
         cord; opposes physiological effects of the sympathetic
         nervous system: stimulates digestive secretions; slows the
         heart; constricts the pupils; dilates blood vessels [syn:
         parasympathetic nervous system, parasympathetic]