·vt To form or pronounce as a diphthong; diphthongize.
II. 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.
III. 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.