From Longman Dictionary of Contemporary Englishdiphthongdiph‧thong /ˈdɪfθɒŋ, ˈdɪp- $ -θɒːŋ/ noun [countable] technical SLa vowel sound made by pronouncing two vowels quickly one after the other. For example, the vowel sound in ‘main’ is a diphthong.
Examples from the Corpus
diphthong• The sounds of hate, bee, high, bone, few, are the basic diphthongs.• You may have noticed that I have not suggested any intensive practice specifically on vowels or their different combinations into diphthongs.• In 1835 the oi diphthong was systematically changed to ai in accordance with modern pronunciation in words like françois.• A frequent fault is making the diphthongs too long: each element is too clearly articulated.• The next two diphthongs are almost exactly the opposite of each other and therefore less likely to be confused.Origin diphthong (1400-1500) French Late Latin diphthongus “two sounds”, from Greek phthongos “voice, sound” 