Diaeresis

n.	1.	(Gram.) The separation or resolution of one syllable into two; - the opposite of synæresis.
	2.	A mark consisting of two dots [as, coöperate, aërial.

Noun

1.

diaeresis - a diacritical mark (two dots) placed over a vowel in German to indicate a change in sound Synonyms: dieresis, umlaut

diacritic, diacritical mark, dieresis, umlaut