um·laut / ˈoŏmˌlout/ Linguistics • n. a mark ( ¨ ) used over a vowel, as in German or Hungarian, to indicate a different vowel quality, usually fronting or rounding. ∎  (esp. in Germanic languages) the process by which a back vowel becomes front in the context of another front vowel, resulting, e.g., in the differences between modern German Mann and Männer or (after loss of the inflection) English man and men.• v. [tr.] modify (a form or a sound) by using an umlaut.

umlaut 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 or (after loss of the inflection) English man and men.

umlaut (philol.) change in the sound of a vowel due to partial assimilation to an adjacent sound. XIX. — G., f. um- about + laut sound.