母音變換
Ablaut \Ab"laut\, n. [Ger., off-sound; ab off + laut sound.] (Philol.) 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.
ablaut n : a vowel whose quality or length is changed to indicate linguistic distinctions (such as sing sang sung song)