(linguistics) A phonological process involving vowels in some languages, setting constraints on what vowels (e.g. front/back vowels only) may be found near each other and sometimes in the entire word.
Sumerian has a system of vowel harmony strikingly like that seen in all modern agglutinative languages, and it has also vocalic dissimilation similar to that found in modern Finnish and Esthonian.
Vocalic harmony is the internal bringing together of vowels of the same class for the sake of greater euphony, while vocalic dissimilation is the deliberate insertion of another class of vowels, in order to prevent the disagreeable monotony arising from too prolonged a vowel harmony.
It does include a box on present tense verb conjugation (taking vowel harmony into account!