Diph"thong [L. diphthongus, Gr. ; = twice + voice, sound, fr. to utter a sound: cf. F. diphthongue.] Orthoepy (a)
A coalition or union of two vowel sounds pronounced in one syllable; as, ou in out, oi in noise; -- called a proper diphthong.
(b)
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.
© Webster 1913.
Diph"thong, v. t.
To form or pronounce as a diphthong; diphthongize.
[R.]
© Webster 1913.