noun
triphthong
A linguistic term for a vowel sound that glides through three distinct qualities within a single syllable.
英語の「fire」の母音は三重母音の例として挙げられることがある。
The vowel in English 'fire' is sometimes cited as an example of a triphthong.
Compound of 三重 (さんじゅう, 'triple') and 母音 (ぼいん, 'vowel'), a straightforward calque of the English term 'triphthong'.