Source : Webster's Revised Unabridged Dictionary (1913)

Miocene \Mi"o*cene\, a. [Gr. ? less + ? new, fresh, recent.]
   (Geol.)
   Of or pertaining to the middle division of the Tertiary. --
   n. The Miocene period. See {Chart} of {Geology}.

Source : WordNet®

Miocene
     n : from 25 million to 13 million years ago; appearance of
         grazing mammals [syn: {Miocene epoch}]