An umlaut is a symbol that is written over vowels in German and some other languages to indicate the way in which they should be pronounced. For example, the word 'für' has an umlaut over the 'u'.
umlaut in British English
(ˈʊmlaʊt)
noun
1.
the mark (¨) placed over a vowel in some languages, such as German, indicating modification in the quality of the vowel
Compare diaeresis
2.
(esp in Germanic languages) the change of a vowel within a word brought about by the assimilating influence of a vowel or semivowel in a preceding or following syllable
Word origin
C19: German, from um around (in the sense of changing places) + Laut sound
umlaut in American English
(ˈʊmlaʊt)
noun Linguistics
1.
a.
a historical change in the sound of a vowel, caused by its assimilation to another vowel or semivowel originally occurring in the next syllable but later sometimes lost; mutation: in English, the differences of vowel in certain singulars and plurals (Ex.: foot—feet, mouse—mice) or in certain causative verbs and the words from which they are derived (Ex.: gold—gild) are due to the effects of umlaut on the second word of each pair
b.
a vowel resulting from such assimilation
2.
the diacritical mark (¨) placed over a vowel, esp. in German, to indicate umlaut
see also dieresis
verb transitive
3.
to modify the sound of (a vowel) or write (a vowel) with an umlaut
Word origin
Ger, change of sound (< um, about + laut, sound, akin to loud): coined (1774) by F. G. Klopstock (1724-1803), Ger poet, but first used in special senses by Jakob Grimm (1819)