Disjoint, somehow, after it's cut the mustard (5)

I believe the answer is:

dijon

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'mustard' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's a link between them I don't understand?

I cannot understand how the remainder of the clue works.

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(Other definitions for dijon that I've seen before include "Source of mustard" , "French town known for mustard" , "French city renowned for mustard" , "French city associated with mustard" , "French city - type of mustard" .)

I've seen this clue in the Sydney Morning Herald.

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