umlaut

/ˈʊm.laʊt/

Borrowed from German Umlaut in the 19th century, from um- or um (“around, re-, trans-”) + Laut (“sound”), from Old High German hlūt. More at loud.

1(linguistics) An assimilatory process whereby a vowel is pronounced more like a following vocoid that is separated by one or more consonants.
2(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 lūsiz > Old English lȳs(i) > Modern English lice).
3(linguistics