Horse galloped round circle (4)
I believe the answer is:
Here is my best explanation:
'horse' is the definition.
(roan is a kind of horse)
'galloped round circle' is the wordplay.
'galloped' becomes 'ran' (I've seen this in other clues).
'round' is an insertion indicator.
'circle' becomes 'o'.
'ran' enclosing 'o' is 'ROAN'.
(Other definitions for roan that I've seen before include "(Horse) white-sprinkled coat", "Type of 17's coat colouring", "Reddish-coloured horse", "nag", "Of horse, with coat sprinkled with white or grey hairs", "Horse with reddish-brown coat", "Nora (anag) - horse", "Horse with coat sprinkled with white or grey hairs", "Bay horse with white/grey hairs in its coat" and "Bay spotted".)