Pound sound at Epsom? (6)

I believe the answer is:

nicker

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'pound' is the definition.
(nicker can informally mean pound sterling)

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

Can you help me to learn more?

(Other definitions for nicker that I've seen before include "Someone who steals (a pound?)" , "One stealing" , "GBP1 (slang)" , "One steals" , "Sound made by horse" .)

I've seen this clue in The Independent.

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