Aspersion on the staff perhaps (4)

I believe the answer is:

slur

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'aspersion' is the definition.
(I know that aspersion can be written as slur)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for slur that I've seen before include "Slight - drawl" , "Innuendo" , "Speak indistinctly, as a drunk might" , "Disparage" , "Discredit to one's reputation" .)

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

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