Diphthongize
[difθɒŋgaiz]
Definition
(verb.) change from a simple vowel to a diphthong; 'This vowel diphthongized in Germanic'.
Checked by Conan--From WordNet
Definition
(v. t. & i.) To change into a diphthong, as by affixing another vowel to a simple vowel.
Typist: Mag