umlaut
noun
°(linguistics) An assimilatory process whereby a vowel is pronounced more like a following vocoid that is separated by one or more consonants.
°(linguistics) The umlaut process (as above) that occurred historically in Germanic languages whereby back vowels became front vowels when followed by syllable containing a front vocoid (e.g. Germanic lūsi > Old English līs(i) > Modern English lice).
verb
°To place an umlaut over a vowel.
synonyms: trema, vowel harmony