Tim Reed's foolish fault (7)
I believe the answer is:
demerit
'fault' is the definition.
(synonyms)
'tim reed's foolish' is the wordplay.
'foolish' indicates anagramming the letters (a foolish spelling).
'tim'+'reed'='timreed'
'timreed' anagrammed gives 'DEMERIT'.
(Other definitions for demerit that I've seen before include "Something deserving censure" , "Conduct that deserves censure" , "Mark given for a fault" , "Fault, defect" , "Black mark" .)