ablaut
n. உள்ளுயிர் மாற்றம்.
Ab"laut, n. Etym: [Ger., off-sound; ab off + laut sound.] (Philol.) Defn: The substitution of one root vowel for another, thus indicating a corresponding modification of use or meaning; vowel permutation; as, get, gat, got; sing, song; hang, hung. Earle.