from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A vowel change, characteristic of Indo-European languages, that accompanies a change in grammatical function; for example, i, a, u in sing, sang, sung. Also called gradation.
from the GNU version of the Collaborative International Dictionary of English
- n. 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.
from The Century Dictionary and Cyclopedia
- n. In philology, a substitution of one vowel for another in the body of the root of a word, accompanying a modification of use or meaning: as, bind, band, bound, bond, German bund; more especially, the change of a vowel to indicate tense-change in strong verbs, instead of the addition of a syllable (-ed), as in weak verbs: as, get, gat, got; sink, sank, sunk.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a vowel whose quality or length is changed to indicate linguistic distinctions (such as sing sang sung song)
German : ab, off (from Middle High German ab, abe, from Old High German aba; see apo- in Indo-European roots) + Laut, sound (from Middle High German lūt, from Old High German hlūt; see kleu- in Indo-European roots).(American Heritage® Dictionary of the English Language, Fourth Edition)
From German Ablaut ("off-sound"), from ab ("off"), + Laut ("sound"). (Wiktionary)