Wears out (5)
I believe the answer is:
tires
'wears out' is the definition.
('tire' can be a synonym of 'wear out')
This is the entire clue.
(Other definitions for tires that I've seen before include "Wearies" , "Grows weary of rites" , "Exhausts" , "Becomes weary and in need of rest" , "Weakens" .)