Derby feature (4)
I believe the answer is:
brim
'derby feature' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for brim that I've seen before include "The edge of a cup or glass" , "Lip of bowl, cup etc" , "Top edge of cup etc" , "'Edge, like that of a hat (4)'" , "Top edge of something" .)