a vowel whose quality or length is changed to indicate linguistic distinctions (such as sing sang sung song)
The substitution of one root vowel for another, thus indicating a corresponding modification of use or meaning; vowel permutation, distinct from the phonetic influence of a succeeding vowel.
To undergo a change of vowel.
The word "ablaut" comes from German Ablaut, meaning "sound gradation." It combines the prefix ab-, indicating deviation or variation, with Laut, which means sound.