Mark over certain German vowels (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" , "Mark indicating changed vowel value in German" , "Mark put over a vowel in German to indicate a different quality" , "Dots over letter (indicating vowel change)" , "Diacritical sign" .)

I've seen this clue in The Times.

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