vt to form or pronounce as a diphthong; diphthongize.
2. diphthong ·noun a coalition or union of two vowel sounds pronounced in one syllable; as, ou in out, oi in noise;
called a proper diphthong.
3. diphthong ·noun a vowel digraph; a union of two vowels in the same syllable, only one of them being sounded; as, ai in rain, eo in people;
called an improper diphthong.