Being out of pocket in short month, drink one beer that’s reduced (9)

I believe the answer is:

marsupial

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But I can't explain it at all! Could you help me understand?

(Other definitions for marsupial that I've seen before include "Kangaroo, etc." , "Pouched animal" , "Sort of animal" , "Kangaroo, for example" , "Joey maybe" .)

I've seen this clue in The Guardian.

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