[n] the 3rd syllable of a word counting back from the end
Misc. Definitions
\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.