U-mutation, or u-umlaut, can refer to various processes that occurred in the history of some
Germanic languages:
*
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
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