Source : Webster's Revised Unabridged Dictionary (1913)

Cerebellum \Cer`e*bel"lum\, n.; pl. E. {Cerebellums}, L.
   {Cerebella}. [L., dim. of cerebrum brain.] (Anat.)
   The large lobe of the hind brain in front of and above the
   medulla; the little brain. It controls combined muscular
   action. See {Brain}.

Source : WordNet®

cerebellum
     n : a major division of the vertebrate brain; situated above the
         medulla oblongata and beneath the cerebrum in humans
     [also: {cerebella} (pl)]