German, coined 1819 by Jakob Grimm from ab off + Laut sound
ablaut in American English
(ˈæbˌlaʊt; ˈɑbaʊt; German ˈɑpˌlaʊt)
noun
patterned change of base vowels in forms of a word or in related words to show changes in tense, meaning, etc., as in the Indo-European languages (Ex.: drink, drank, drunk)