- Phonetics. an unsegmentable, gliding speech sound varying continuously in phonetic quality but held to be a single sound or phoneme and identified by its apparent beginning and ending sound, as the oi-sound of toy or boil.
- (not in technical use)
- a digraph, as the ea of meat.
- a ligature, as æ.
verb (used with or without object)
- to diphthongize.
- a vowel sound, occupying a single syllable, during the articulation of which the tongue moves from one position to another, causing a continual change in vowel quality, as in the pronunciation of a in English late, during which the tongue moves from the position of (e) towards (ɪ)
- a digraph or ligature representing a composite vowel such as this, as ae in Caesar
late 15c., from Middle French diphthongue, from Late Latin diphthongus, from Greek diphthongos “having two sounds,” from di- “double” (see di- (1)) + phthongos “sound, voice,” related to phthengesthai “utter, speak loudly.”