Cowboy's money put on a jumper (8)

I believe the answer is:

buckaroo

'cowboy's' is the definition.
(buckaroo is a kind of cowboy)

'money put on a jumper' is the wordplay.
'money put' becomes 'buck' (I am not sure about this - if you are sure you should believe this answer much more).
'on' says to put letters next to each other.
'jumper' becomes 'roo' (I've seen this before).
'buck'+'a'+'roo'='BUCKAROO'

(Another definition for buckaroo that I've seen is " cowboy".)

I've seen this clue in The Guardian.

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