Ablaut

Ablaut is a process by which an inflected form of a word is formed by changing the vowel of the base. In the narrower sense, Ablaut refers to the system of root vowel alternations in Proto-Indo-European and its daughter languages.

Example
in English it is possible to derive the past tense of strong verbs by substituting the base vowel by another vowel: get : got, sing :sang and fall :fell.

Ablaut in Proto-Indo-European
There existed the following variants or "grades" of ablaut:


 * full grade, or "e" grade,
 * full grade with ablaut, or "o" grade
 * lengthened grade
 * lengthened grade with ablaut
 * zero grade.

The results of this alternation can be seen in the following related words of modern English (listed in the same order as the above grades): sit, sat, seat, soot, nest; and also in the English strong verb system.

Synonyms

 * metaphony, gradation

Origin
The term ablaut was borrowed from German Ablaut, coinded by Jacob Grimm in the early part of the 19th century.

Other languages
French métaphonie German Ablaut (de)

Link
Utrecht Lexicon of Linguistics