This pencil's not for writing (7)

I believe the answer is:

styptic

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'this pencil's not for writing' is the definition.
The definition suggests a singular noun which matches the answer.

This is the entire clue.

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(Other definitions for styptic that I've seen before include "Checking blood flow like shaving pencil" , "Stopping bleeding" , "This pencil checks bleeding as from shaving" .)

I've seen this clue in the Evening Standard.

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