— diphthongal /dif thawng"geuhl, -thong"-, dip-/ , diphthongic, diphthongous , adj.
/dif"thawng, -thong, dip"-/ , 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 ae.
v.t. , v.i.
3. to diphthongize.
[ 1425-75; late ME diptonge diphthongus díphthongos lit., having two sounds ( di- DI- 1 + phthóngos voice, sound) ]