What is the meaning of Umlaut?

An assimilatory process whereby a vowel is pronounced more like a following vocoid that is separated by one or more consonants.

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 lūsiz > Old English lȳs(i) > Modern English lice).

A vowel so assimilated.

The diacritical mark ( ¨ ) placed over a vowel when it indicates a (rounded) front vowel

Synonym of diaeresis

To place an umlaut over (a vowel).

To modify (a word) so that an umlaut is required in it.

umlaut

umlaut (the diacritical mark ( ¨ ) placed over various vowels: a > ä, o > ö or u > ü in German and some closely related languages)

umlaut (partial assimilation of a vowel)

umlaut (vowel so assimilated)

umlaut (diacritical mark)

umlaut

umlaut (the partial assimilation of vowels in some Germanic languages)

umlaut (diacritical mark)

umlaut (the partial assimilation of a vowel in Germanic languages)

umlaut (the diacritical mark ¨ used to indicate such assimilation)

umlaut

Source: wiktionary.org