from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A complex speech sound or glide that begins with one vowel and gradually changes to another vowel within the same syllable, as (oi) in boil or (ī) in fine.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A complex vowel sound that begins with the sound of one vowel and ends with the sound of another vowel, in the same syllable.
- n. A vowel digraph or ligature.
from the GNU version of the Collaborative International Dictionary of English
- n. A coalition or union of two vowel sounds pronounced in one syllable; as, ou in out, oi in noise; -- called a proper 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.
- transitive v. To form or pronounce as a diphthong; diphthongize.
from The Century Dictionary and Cyclopedia
- n. A coalition or union of two vowels pronounced in one syllable.
- To sound as a diphthong; diphthongize.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a vowel sound that starts near the articulatory position for one vowel and moves toward the position for another
Middle English diptonge, from Old French diptongue, from Late Latin diphthongus, from Greek diphthongos : di-, two; see di-1 + phthongos, sound.(American Heritage® Dictionary of the English Language, Fourth Edition)
French diphtongue, from Ancient Greek δίφθογγος (diphthongos, "two sounds"), from δίς (dis, "twice") + φθόγγος (phthongos, "sound"). (Wiktionary)