Well directed it may finish off the game (3)

I believe the answer is:

gun

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'well' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for gun that I've seen before include "It can be carried by 15 Ac" , "Hand weapon" , "Arm" , "Shooter" , "Artillery piece" .)

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

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