Tread-bare (4)
I believe the answer is:
bald
'tread-bare' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bald that I've seen before include "Lacking hair on the scalp" , "Without the natural covering" , "Exposed" , "With the tread worn away" , "With no effort to conceal" .)