"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&q [..]

Jacob Grimm's term for the way in which Old English strong verbs formed their preterites by a vowel change. This is also called gradation. An example would be the principal parts of Old English s [..]

(n) a vowel whose quality or length is changed to indicate linguistic distinctions (such as sing sang sung song)

Pronunciation: ˈæblaʊt The change in the quality of a vowel in a root which is not conditioned by the phonetic context. An example is the vowel change seen in Classical Arabic verbs: write perfect ten [..]

a vowel change that accompanies a change in grammatical function. Same as "gradation." Sing, sang, and sung.

(linguistics) The substitution of one root vowel for another, thus indicating a corresponding modification of use or meaning; vowel permutation; as,andandsubstitution of one root vowel for another [..]

(linguistics) ablaut