Added 10 October 2026 diphthongise verb Categories: LanguageObscure Words verb ! Definition from WordNet 3.1, Princeton University. More about diphthongise at Wordnik → Where our words come from → Change from a simple vowel to a diphthong. This vowel diphthongized in Germanic Related Words: diphthongizemonophthongisemonophthongizetransphonologisephonemicisephonemicizevowelisediazotisedualisephoneticizedentalisepinyinise Back to today's word