Hat feature (4)
I believe the answer is:
brim
'hat feature' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for brim that I've seen before include "'Edge, like that of a hat (4)'" , "Peak (of cap); be very full" , "Be full; edge of hat" , "Topmost edge" , "Lip; part of 6 Down" .)