Pronunciation: (dif'thông, -thong, dip'-),[key] —n. 1. Phonet.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. 2. (not in technical use)
a. a digraph, as the ea of meat. b. a ligature, as æ.