Dots over the vowel in Köln (6)

I believe the answer is:

umlaut

(Other definitions for umlaut that I've seen before include "Two dots put over a vowel in German" , "Diacritical sign" , "Mark over some German letters" , "German accent" , "Diacritical mark (two dots) placed over a vowel in German to indicate a change in sound" .)

I've seen this clue in The Guardian.

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