TRIPHTHONG Meaning of TRIPHTHONG in English [triph.thong] n [tri- + -phthong (as in diphthong)] (ca. 1599) 1: a phonological unit consisting of three successive vocalic sounds in one syllable 2: trigraph -- triph.thon.gal adj Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012