diphthongal


diph·thong

D0238300 (dĭf′thông′, -thŏng′, dĭp′-)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.
[Middle English diptonge, from Old French diptongue, from Late Latin diphthongus, from Greek diphthongos : di-, two; see di-1 + phthongos, sound.]
diph·thon′gal adj.