Crossword Genius

What hounds may do for a horse? (3)

Ross

I believe the answer is:

bay

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

'horse?' is the definition.
(I know that bay is a type of horse)

'what hounds may do for a' is the wordplay.
I cannot really see how this works, but
'a' is found in the answer.
The remaining letters 'by' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for bay that I've seen before include "Howl" , "Tree; horse; bark loudly" , "Indentation of a shoreline" , "Sea inlet" , "Inlet, cove" .)

I've seen this clue in the Evening Standard.
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