ablaut; vowel gradation; apophony
Linguistic term for systematic vowel changes within a root, such as sing/sang/sung. Rare in general use; mainly encountered in academic contexts.
Ablaut can be seen in English irregular verbs.
vowel shift
Refers to a historical or systematic change in vowel pronunciation, such as the Great Vowel Shift. Also a technical term.
The Great Vowel Shift is an example of a vowel shift in English.