Source : Webster's Revised Unabridged Dictionary (1913)

Antepenult \An`te*pe"nult\, Antepenultima \An`te*pe*nult"i*ma\,
   n. [L. antepaenultima (sc. syllaba) antepenultimate; ante
   before + paenultimus the last but one; paene almost + ultimus
   last.] (Pros.)
   The last syllable of a word except two, as -syl- in
   monosyllable.

Source : WordNet®

antepenult
     n : the 3rd syllable of a word counting back from the end [syn:
         {antepenultimate}]