Definition from Wiktionary, the free dictionary
Alternative forms 
antepenultimate (not comparable)
- Two before the last, i.e., the one immediately before the penultimate, in a series.
- This book has ten chapters — chapter 8 is the antepenultimate one.
- (of a syllable) Last but two; third from last.
Coordinate terms 
- (adjectives denoting syllables): ultimate (last), penultimate (last but one), preantepenultimate (last but three), propreantepenultimate (last but four)
two before the last
antepenultimate (plural antepenultimates)
- Two before the last in a series. e.g. (..., antepenultimate, penultimate, ultimate)
- The syllable that comes two before the last in a word.
- The words animal, citizen, comedy, dangerous, and obvious are stressed on the antepenultimate.