Horse cooked in casserole wife chucked out (5)

I believe the answer is:

steed

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'horse' is the definition.
(steed is a kind of horse)

I can't explain the rest of the clue.

(Other definitions for steed that I've seen before include "Swift horse" , "Powerful horse" , "Horse, mount" , "(Poetic) horse" , "A mount (poet.)" .)

I've seen this clue in The Sun, The Times and The Telegraph.

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