A tailor may make his mark with it (6,5)

I believe the answer is:

french chalk

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'a tailor may make his mark with it' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

This is all the clue.

Can you help me to learn more?

(Other definitions for french chalk that I've seen before include "Marker" , "Soft compact talc used for marking cloth" .)

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

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