The Collaborative International Dictionary of English v.0.48:

neocortex \neocortex\ n.
   The cortical part of the neencephalon; the most recently
   evolved part of the cerebral cortex of the brain of higher
   animals, and the site of most of the higher brain functions;
   called also neopallium.

   Syn: neopallium.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

neocortex
    n 1: the cortical part of the neencephalon [syn: neopallium,
         neocortex]