Discourage venison suppliers heartlessly! (5)

I believe the answer is:

deter

I'm a little stuck... Click here to teach me more about this clue!

'discourage' is the definition.
(I know that discourage can be written as deter)

I can't explain the rest of the clue.

(Other definitions for deter that I've seen before include "'Discourage, dissuade (5)'" , "Hinder, prevent" , "Inhibit" , "Hinder, discourage" , "Warn off" .)

I've seen this clue in the Evening Standard.

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