The horse galloped around for nothing (4)
I believe the answer is:
roan
'the horse' is the definition.
(roan is a kind of horse)
'galloped around for nothing' is the wordplay.
I cannot really see how this works, but
'around' could be 'o' (a round letter) and 'o' is present in the answer.
'galloped' could be 'ran' (I've seen this in another clue) and 'ran' is found in the remaining letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for roan that I've seen before include "nag" , "Horse with a brownish coat sprinkled with grey" , "Horse - leather" , "Horse with reddish-brown coat" , "Horse with coat speckled with white or grey" .)