Also 7 triphthonge, tripthong, 8 triphthongue. [f. TRI-, after DIPHTHONG; cf. F. triphtongue (1550 in Godef., Compl.).] A combination of three vowel sounds in one syllable; also loosely applied to a combination of three vowel characters, more correctly called TRIGRAPH. (Cf. DIPHTHONG.)
1599. Minsheu, Span. Gram. (1623), 9. A triphthong is a sounding of three vowels into one syllable with one breath together, and that after five sorts.
a. 1637. B. Jonson, Eng. Gram., I. v. The Tripthong is of a complexion, rather to be fear’d than lov’d.
1668. Wilkins, Real Char., 371. A common Assertion … That no one syllable can consist of three Vowels, and consequently that there can be no Tripthongs.
1706. Phillips (ed. Kersey), Triphthongue.
1711. J. Greenwood, Eng. Gram., 244. A Triphthong is, when three Vowels meet together in one Syllable; as eau in Beauty: but this we pronounce Buty.
1889. Pitman, Man. Phonogr. (new ed.), § 41. The double vowels heard in the words ice, owl, ay, boy, and the triphthong wī, are represented by small angular marks.
Hence Triphthongal a., pertaining to or of the nature of a triphthong.
1748. Phil. Trans., XLV. 403. 7 vocal Notes or Vowels,… struck, as one may say, in diphthongal or triphthongal Chords with each other.
