Diphthongize
/ˈdɪfθɔːŋaɪz,ˈdɪpθɔːŋaɪz/
Definition 1 of 1
Pro Tip 1/3Pronunciation Dynamics
Understanding 'diphthongize' helps you spot subtle changes in vowel pronunciation across different accents or dialects. 
Learning British English made me realize they often diphthongize the vowel in 'no.'
Pro Tip 2/3Accent Variation
'Diphthongize' is key to mimic accents since many accents involve diphthongization of certain vowel sounds. 
To sound Australian, you have to diphthongize the word 'mate' to something like 'maite'.
Pro Tip 3/3Historical Language Change
Diphthongization can signal historical changes in language pronunciation over time. 
Scholars studied how Latin words diphthongized as they evolved into the Romance languages.