U-mutation

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