A triphthong is a sequence of three vowels making up one syllable.    From Wordnik.com.  [Triphthongs in Spanish] Reference

The union of three vowels in one sound is called a triphthong; as iew in view.    From Wordnik.com.  [The Standard Speller; Containing Exercises for Oral Spelling; also, Sentences for Silent Spelling by Writing from Dictation. In Which the Representative Words and the Anomalous Words of the English Language are so Classified as to Indicate Their Pronunciation, and to be Fixed in the Memory by Association.] Reference

A triphthong is PROPER if all three of the vowels are sounded.    From Wordnik.com.  [Orthography As Outlined in the State Course of Study for Illinois] Reference

For a triphthong to exist, two closed atonic vowels (“i” or “u”) and, between them, an open vowel (“a”, “e”, or “o”): anunciáis, guau, miau, confiéis.    From Wordnik.com.  [Triphthongs in Spanish] Reference

However, for purposes of graphic accenting, any sequence made up of an open vowel between two closed atonic vowels will always be considered as a triphthong, regardless of its actual articulation in one or two syllables.    From Wordnik.com.  [Triphthongs in Spanish] Reference

A sequence of atonic closed vowel + open vowel + atonic closed vowel can be pronounced, in certain cases, as one syllable, a triphthong, and in others as two distinct syllables, with a hiatus followed by a diphthong, or vice versa.    From Wordnik.com.  [Triphthongs in Spanish] Reference

Only the first two of these four words contain a triphthong.    From Wordnik.com.  [Frederic Mistral]

Within a word two or three contiguous vowels usually combine to form a diphthong or a triphthong respectively.    From Wordnik.com.  [Modern Spanish Lyrics] Reference

TrIfhoghar, a triphthong.    From Wordnik.com.  [Focalóir gaoidhilge-sax-bhéarla, or An Irish-English dictionary. Whereof the Irish part hath been compiled not only from various Irish vocabularies, particularly that of Mr. Edward Lhuyd; but also from a great variety of the best Irish manuscripts now extant ..] Reference

15. triphthong.    From Wordnik.com.  [A Spelling-Book for Advanced Classes] Reference

O is often us’d for a triphthong (y in British).    From Wordnik.com.  [Magazine, or Animadversions on the English Spelling (1703)] Reference

Tags: atonic, closed vowel, diphthong, grammar, open vowel, pronunciation, Real Academia Española, Spanish, tonic, triphthong, vowels.    From Wordnik.com.  [Triphthongs in Spanish] Reference