One aiming at a fast buck or deer (4)

I believe the answer is:

stag

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'deer' is the definition.
(stag is a kind of deer)

I don't understand how the remainder of the clue works.

(Other definitions for stag that I've seen before include "Stock Exchange speculator standing" , "Investor" , "one may get in a rut" , "Male deer; speculator" , "Game - speculator" .)

I've seen this clue in The Times.

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