Having been changed into or currently pronounced as a diphthong; having undergone diphthongization.
From 'diphthongize' (American verb) + '-d' (past tense/adjectival). This describes the completed state or ongoing characteristic of vowels that have transformed into diphthongal sounds.
When you see a vowel in a linguistic journal marked as 'diphthongized,' scientists are tracking how language itself is literally changing in real-time through how people's mouths move differently!
Complete word intelligence in one call. Free tier — 50 lookups/day.