1. to convert a vowel sound into a diphthong; to pronounce or write as a diphthong
Usage: British English spelling (American English: diphthongizes); linguistics, phonetics

Examples

• The linguist explained how certain dialects diphthongises the vowel sound in 'face'.
• Over time, the language diphthongises several of its original monophthongs.
• Modern English diphthongises vowels that were once pronounced as single sounds in Middle English.
• The phonetic system diphthongises the stressed vowels in specific contexts.