Fault (7)
'fault' is the definition.
(synonyms)
This is all the clue.
(Other definitions for demerit that I've seen before include "Black mark" , "Conduct that deserves censure" , "Fault, defect" , "Something deserving censure" , "Feature deserving censure" .)
'fault' is the definition.
(I know that fault can be written as error)
This is the entire clue.
(Other definitions for error that I've seen before include "Solecism" , "Mistake from terrorist" , "Miscarriage of justice" , "Blunder, slip" , "Mistake or fault" .)
'fault' is the definition.
(synonyms)
This is all the clue.
(Other definitions for flaw that I've seen before include "(Make) defect(ive)" , "Imperfection or blemish" , "Mark, blemish" , "Fault, blemish" , "Defect, imperfection" .)