Axe to cause devastation (4)

I believe the answer is:

sack

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'axe' is the definition.
(both can mean to dismiss or fire)

I can't explain the remainder of the clue.

(Other definitions for sack that I've seen before include "Large canvas bag" , "Receptacle" , "Fire the large bag?" , "See 12" , "boot" .)

I've seen this clue in The Everyman puzzle in The Observer.

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