A tool in pieces (6)

I believe the answer is:

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

I don't understand the remainder of the clue.

(Other definitions for jigsaw that I've seen before include "Kind of puzzle" , "Puzzle with pieces to assemble" , "Problem with fitting in" , "As pastime" , "Puzzle - powered cutter" .)

I've seen this clue in the Evening Standard.

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