triphthong

noun2

1. •
   A monosyllabic vowel combination usually involving a quick but smooth movement from one vowel to another that passes over a third one.

   • In Lang Belta vowels usually appear preceding or following a consonant (see previous examples), and as of now no occurrence of diphthongs or triphthongs has been attested. — 2021
2. •
   A disyllabic sequence of a vowel, a semivowel, and a vowel.