Triphthong
In phonetics, a triphthong is a monosyllabic vowel combination involving a quick but smooth movement of the articulator from one vowel quality to another that passes over a third. While "pure" vowels, or monophthongs, are said to have one target articulator position, diphthongs have two and triphthongs three.
In English, there are only two triphthongs: /aʊə/ as in the word “hour” and /aɪə/ as in the word “fire”. Triphthongs are less common in English than vowels, but they are still an important part of the language.
Triphthong. Vocabulary.com, Dictionary, Vocabulary.com, https://www.vocabulary.com/dictionary/triphthong.
Bathia,T.K .(2003).Punjabi: A Cognitive-Descriptive Grammar. (341)
Definition of triphthong from the Collins English Dictionary https://www.collinsdictionary.com/dictionary/english.