Animal possibly reined (4)

I believe the answer is:

deer

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'animal' is the definition.
(deer is a type of animal)

I cannot understand how the remainder of the clue works.

(Other definitions for deer that I've seen before include "The - Hunter, 1978 film" , "See 23" , "The male has antlers" , "Red, roe or fallow" , "Ruminant(s) -- breed of 13 down" .)

I've seen this clue in the Evening Standard.

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