Triphthong

A triphthong is a type of vowel sequence in which the syllable’s nucleus changes quality through three distinct vowel targets during a single syllable. In practice, a triphthong is treated as a three-part glide rather than as two separate vowels in sequence.

This concept is contrasted with a monophthong (a single, stable vowel), a diphthong (two vowel qualities within the nucleus), and hiatus (two vowels occurring in adjacent syllables). Whether a particular three-vowel sequence is analyzed as a true triphthong or as a diphthong plus a schwa or a similar combination can depend on the language and the analysis used by linguists.

In English, several dialects are described as containing triphthongs in common words such as fire, liar, and layer, where the sequence may be transcribed as /faɪə/, /laɪə/, and /leɪə/. Some analyses view these as true triphthongs, while others prefer analyses in which the sounds are a diphthong followed by a reduced vowel or a rhotacized vowel, depending on dialect and speaker. The existence and character of triphthongs in English are thus subject to debate among phoneticians.

Beyond English, triphthongs have been described in discussions of other languages and dialects, though they are relatively rare and the specific analyses vary. The term itself derives from Greek, with tri- meaning three and phthongos meaning sound or voice.