Medieval horse, black, with three feet? (6)

I believe the answer is:

bayard

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'medieval horse' is the definition.
The definition suggests a singular noun which matches the answer.

'black with three feet?' is the wordplay.
'black with' becomes 'ba' (I can't justify this - if you can you should give a lot more credence to this answer).
'three feet?' becomes 'yard' (I've seen this before).
'ba'+'yard'='BAYARD'

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I've seen this clue in The Times.

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