umlaut (n.)
1852, from German umlaut "change of sound," from um "about" (see ambi-) + laut "sound," from Old High German hlut (see listen). Coined 1774 by poet Friedrich Gottlieb Klopstock (1724-1803) but first used in its current sense "modification of vowels" 1819 by linguist Jakob Grimm (1785-1863).