The Collaborative International Dictionary of English v.0.48:

central nervous system \central nervous system\ n.
   the portion of the vertebrate nervous system consisting of
   the brain and spinal cord; -- abbreviated CNS.

   Syn: CNS.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

central nervous system
    n 1: the portion of the vertebrate nervous system consisting of
         the brain and spinal cord [syn: central nervous system,
         CNS, systema nervosum centrale]