Source : Webster's Revised Unabridged Dictionary (1913)

Paleozoic \Pa`le*o*zo"ic\, a. [Paleo- + Gr. ? life, fr. ? to
   live.] (Geol.)
   Of or pertaining to, or designating, the older division of
   geological time during which life is known to have existed,
   including the Silurian, Devonian, and Carboniferous ages, and
   also to the life or rocks of those ages. See Chart of
   {Geology}.

Source : WordNet®

Paleozoic
     n : from 544 million to about 230 million years ago [syn: {Paleozoic
         era}]