Philol. [mod. Germ., f. ab off + laut sound.] Vowel permutation; systematic passage of the root vowel into others in derivation, as in sing, sang, song, sung, apart from the phonetic influence of a succeeding vowel as in Umlaut.
1871. Earle, Philol. Eng. Tong., § 124 (1880). But it was in the verbal conjugation that the Ablaut found its peculiar home, and there it took formal and methodical possession.
