Source : Webster's Revised Unabridged Dictionary (1913)

Antepenultimate \An`te*pe*nult"i*mate\, a.
   Of or pertaining to the last syllable but two. -- n. The
   antepenult.

Source : WordNet®

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