diphthongize(v = verb.communication) diphthongise - change from a simple vowel to a diphthong; "This vowel diphthongized in Germanic"
is one way to change, shift, switch
Derived form noun diphthong₁
Sample sentences: Something ----s

diphthongize, v.tr. (also -ise) pronounce as a diphthong.

Derivative:
diphthongization n.