Two before the last, i.e., the one immediately before the penultimate, in a series.

Two before the last in a series. e.g. (..., antepenultimate, penultimate, ultimate) / The syllable that comes two before the last in a word.

Second from the last in serial order.

plural of antepenultimate

= antepenult, antepenultima / (rare) Antepenultimate position. / (rare) Any thing occurring as the antepenultimate item in a series.