Pronunciation: (äb'lout, ab'-; Ger. äp'lout), [key]
(in Indo-European languages) regular alternation in the internal phonological structure of a word element, esp. alternation of a vowel, that is coordinated with a change in grammatical function or combination, as in English sing, sang, sung, song; apophony.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.