Source : Webster's Revised Unabridged Dictionary (1913)

Penult \Pe"nult\, n. [Abbreviated fr. penultima.] (Gram. &
   Pros.)
   The last syllable but one of a word; the syllable preceding
   the final one.

Source : WordNet®

penult
     n : the next to last syllable in a word [syn: {penultima}, {penultimate}]