Relating to or containing a diphthong; having the characteristics of a diphthong.
From 'diphthong' + '-al' (relating to). This adjectival form emerged in linguistic terminology to describe sounds and pronunciations with diphthongal qualities.
Modern English has far more diphthongs than many languages—compare the 'oa' in 'boat' with how Spanish speakers say the same vowel sound, which is crisp and pure instead of gliding!
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