English▸ noun a mark (¨) used over a vowel, especially in German, to indicate a different vowel quality.
▪ [mass noun] the process in Germanic languages by which the quality of a vowel was altered in certain phonetic contexts, resulting for example in the differences between modern German Mann and Männer.
▸ verb [with object] modify (a form or sound) by using an umlaut:
the colour of prothetic vowels, unless umlauted by the next syllable, was that of the laryngeal which was vocalized.
– ORIGIN mid 19th century: from German Umlaut, from um ‘about’ + Laut ‘sound’.