Diphthong

n.	1.	(Orthoëpy) A coalition or union of two vowel sounds pronounced in one syllable; as, ou in out, oi in noise; - called a proper diphthong.
v. t.	1.	To form or pronounce as a diphthong; diphthongize.

Noun

1.

diphthong - a vowel sound that starts near the articulatory position for one vowel and moves toward the position for another

allophone, alveolar, apico-alveolar, apico-dental, articulation, aspiration, assimilation, bilabial, cacuminal, cerebral, check, consonant, continuant, dental, dissimilation, epenthetic vowel, explosive, glide, glottal, glottalization, guttural, labial, labialization, labiodental, labiovelar, laryngeal, lateral, lingual, liquid, manner of articulation, modification, monophthong, morphophoneme, mute, nasal, occlusive, palatal, parasitic vowel, peak, pharyngeal, pharyngealization, phone, phoneme, plosive, prothetic vowel, retroflex, segmental phoneme, semivowel, sonant, sonority, speech sound, stop, surd, syllabic nucleus, syllabic peak, syllable, transition sound, triphthong, velar, vocable, vocalic, vocoid, voice, voiced sound, voiceless sound, voicing, vowel