umlaut

UK: /ˈʊmlaʊt/ US: /ˈʊmlaʊt/ ,(ŏŏm′lout)

WordReference Random House Learner's Dictionary of American English © 2025

um•laut /ˈʊmlaʊt/  n. [countable]

1. Linguistics a mark (68¨62) used as a marker over a vowel, as ä, ö, ü, to indicate a vowel sound different from that of the letter without the mark, esp. as used in German.

WordReference Random House Unabridged Dictionary of American English © 2025

um•laut  (ŏŏm′lout), [Ling.]
n. 

1. a mark (¨) used as a diacritic over a vowel, as ä, ö, ü, to indicate a vowel sound different from that of the letter without the diacritic, esp. as so used in German. Cf. dieresis. 
2. (in Germanic languages) assimilation in which a vowel is influenced by a following vowel or semivowel;
   apophony.

v.t. 

3. to modify by umlaut.
4. to write an umlaut over.

• German, equivalent. to um- about (i.e., changed) + Laut sound
• 1835–45

Collins Concise English Dictionary © HarperCollins Publishers::

umlaut / 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

Etymology: 19th Century: German, from um around (in the sense of changing places) + Laut sound