'umlaut' definitions:

Definition of 'umlaut'

noun

A diacritical mark (two dots) placed over a vowel in German to indicate a change in sound [syn: umlaut, dieresis, diaeresis]

From: GCIDE

umlaut \um"laut\ ([=oo]m"lout), n. [G., from um about + laut sound.] (Philol.) The euphonic modification of a root vowel sound by the influence of a, u, or especially i, in the syllable which formerly followed. [1913 Webster]
Note: It is peculiar to the Teutonic languages, and was common in Anglo-Saxon. In German the umlauted vowels resulting from a, o, u, followed by old i, are written [aum], ["o], ["u], or ae, oe, ue; as, m[aum]nner or maenner, men, from mann, man. Examples of forms resulting from umlaut in English are geese pl. of goose, men pl. of man, etc. [1913 Webster]