Bay tree not wide (4)
I believe the answer is:
roan
'bay' is the definition.
(both are a type of horse)
'tree not wide' is the wordplay.
I cannot really see how this works, but
'not' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
The remaining letters 'ran' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for roan that I've seen before include "nag" , "Type of 17's coat colouring" , "Nora (anag) - horse" , "Horse with a brownish coat sprinkled with grey" , "Horse with brownish coat speckled with white" .)