Real Dictionary

parasympathetic in American English
designating or of that part of the autonomic nervous system whose nerves originate in the midbrain, the hindbrain, and the sacral region of the spinal cord and whose functions include the constriction of the pupils of the eyes, the slowing of the heartbea
adjective: pertaining to that part of the autonomic nervous system consisting of nerves and ganglia that arise from the cranial and sacral regions and function in opposition to the sympathetic system, as in inhibiting heartbeat or contracting the pupil of the eye

parasympathetic in British English
adjective: of or relating to the division of the autonomic nervous system that acts in opposition to the sympathetic system by slowing the heartbeat, constricting the bronchi of the lungs, stimulating the smooth muscles of the digestive tract, etc