Either fire or unload it (9)

I believe the answer is:

discharge

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'either fire' is the definition.
'discharge' can be an answer for 'fire' (synonyms). I am unsure of the 'either' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for discharge that I've seen before include "cashier" , "empty" , "meet" , "Put out" , "Fire (a gun); release from custody" .)

I've seen this clue in the Evening Standard.

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