Diphthong :: Diphthong (n.) A coalition or union of two vowel sounds pronounced in one syllable; as, ou in out, oi in noise; -- called a proper diphthong..
Diphthong :: Diphthong (n.) 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..
Diphthong :: Diphthong (v. t.) To form or pronounce as a diphthong; diphthongize.
Diphthongal :: Diphthongal (a.) Relating or belonging to a diphthong; having the nature of a diphthong.
Diphthongalize :: Diphthongalize (v. t.) To make into a diphthong; to pronounce as a diphthong.