One preparing to shoot a spaniel? (6)

I believe the answer is:

cocker

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'spaniel?' is the definition.
(I know that cocker is a type of spaniel)

I can't explain the remainder of the clue.

(Other definitions for cocker that I've seen before include "Type of spaniel" , "and 12 Down: Dog" , "Breed of spaniel" , "pet" .)

I've seen this clue in the Evening Standard.

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