Antepenult

прилагательное третий слог от конца

Большой англо-русский словарь

Antepenult

also antepenultima noun Etymology: Late Latin antepaenultima, feminine of antepaenultimus preceding the next to last, from Latin ante- + paenultimus penultimate the third syllable of a word counting from the end (as cu in accumulate) • antepenultimate adjective or noun

Merriam-Webster's Collegiate Dictionary