diphthonging

/ˈdɪfθɔŋɪŋ/
noun
  1. The process of pronouncing a vowel sound that glides from one vowel to another within the same syllable.
    • Her accent features noticeable diphthonging, making 'time' sound like 'toim'.
    • The diphthonging in the word 'coin' combines an 'oh' and 'ee' sound.
    • Linguistics students studied the diphthonging of vowels in different English dialects.