'proper diphthong' definitions:

Definition of 'proper diphthong'

From: GCIDE

Diphthong \Diph"thong\ (?; 115, 277), n. [L. diphthongus, Gr. ?; di- = di`s- twice + ? voice, sound, fr. ? to utter a sound: cf. F. diphthongue.] (Ortho["e]py) (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. [1913 Webster]