A slight mark on the music (4)

I believe the answer is:

slur

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This might be a double definition.

'a slight' is the first definition.
(I've seen this before)

'mark on the music' is the second definition.
'slur' can be an answer for 'mark' (thesaurus). I'm not certain of the 'on the music' bit.

Can you help me to learn more?

(Other definitions for slur that I've seen before include "Slight - incoherence in speech" , "Pronounce indistinctly or cast abuse on reputation" , "libel" , "Slight - stain" , "Stigma" .)

I've seen this clue in The Globe and Mail.

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