U-mutation, or u-umlaut, can refer to various processes that occurred in the history of some
Germanic languages
The Germanic languages are a branch of the Indo-European languages, Indo-European language family spoken natively by a population of about 515 million people mainly in Europe, North America, Oceania, and Southern Africa. The most widely spoke ...
:
*
Old Norse u-umlaut, allophones of non-rounded vowels before back rounded vowels being made distinctive around the 8th century
*
Icelandic u-umlaut, a similar process affecting only and operating productively in modern
Icelandic
*
Old English back mutation, a change that took place in late prehistoric Old English
{{disambig