1. The third from the last syllable of a word: The antepenult is stressed as in the words get in for•get•ful•ness; per in su•per•flu•ous; lu in the word an•te•di•lu•vi•an; and ter in an•ter•i•or.
2. Etymology: from Latin ante-, "before" + penult, "next to the last syllable in a word".

Antepenult should be considered the part of a word that precedes the penult, "next to the last syllable" from Late Latin antepaenultima.