n. & v.
--n.
1. a mark used over a vowel, esp. in Germanic languages, to indicate a vowel change.
2 such a vowel change, e.g. German Mann, M{auml}nner, English man, men, due to i, j, etc. (now usu. lost or altered) in the following syllable.
--v.tr. modify (a form or a sound) by an umlaut.
Etymology: G f. um about + Laut sound