ablaut (n.) Look up ablaut at Dictionary.com
"systematic vowel alteration in the root of a word to indicate shades of meaning or tense," a characteristic of Indo-European languages, 1849, from German Ablaut, literally "off-sound" ("off" here denoting substitution), coined by J.P. Zweigel in 1568 from ab "off" (from Old High German aba "off, away from," from PIE root *apo- "off, away;" see apo-) + Laut "sound, tone" (from Old High German hlut; see listen (v.)). The word was popularized by Jacob Grimm. The process is what makes strong verbs in Germanic. An example is bind/band/bond/bound + (German) Bund.