Rite used flag (4)
I believe the answer is:
tire
'flag' is the definition.
(both can mean to become weary)
'rite used' is the wordplay.
'used' indicates an anagram.
'rite' is an anagram of 'TIRE'.
(Other definitions for tire that I've seen before include "Flag" , "Weaken" , "Get weary" , "Wear out" , "Become exhausted" .)