ablaut
/ˈæbˌlaʊt/noun
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The substitution of one root vowel for another, thus indicating a corresponding modification of use or meaning; vowel permutation; as, get and got; sing and song; hang and hung, distinct from the phonetic influence of a succeeding vowel.
Synonyms:
alternation, apophony, gradation
verb
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(of a vowel-containing linguistic component) To undergo a change of vowel.
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To cause to change a vowel.