diph·thong (dĭfthông′, -thŏng′, dĭp-)
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.]
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Indo-European & Semitic Roots Appendices
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