The process or result of converting a pure vowel sound into a diphthong over time.
From 'diphthongize' (American verb) + '-ation'. This noun captures the major linguistic phenomenon where simple vowels develop into gliding vowel sounds across generations.
The Great Vowel Shift—the massive diphthongization that changed English pronunciation 600+ years ago—is why we now pronounce words so differently from how they're spelled, creating spelling nightmares for learners!
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