Fire an employee for drinking perhaps (4)

I believe the answer is:

sack

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'fire' is the definition.
(dismiss someone from their job)

I cannot understand how the rest of the clue works.

(Other definitions for sack that I've seen before include "It carries coal" , "Dismiss (from a job)" , "Marching orders?" , "Plundering of captured town" , "Fire - rifle" .)

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

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