Macbeth's fancied weapon (6)

I believe the answer is:

dagger

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'weapon' is the definition.
(dagger is a kind of weapon)

I cannot understand how the rest of the clue works.

(Other definitions for dagger that I've seen before include "The weapon Macbeth thought he saw" , "''Is this a ... which I see before me'' (Macbeth)" , "Short knife for stabbing" , "Stabbing weapon" , "Macbeth's weapon" .)

I've seen this clue in the Evening Standard.

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