Defective weight or, conversely, any number of grams (5)
I believe the answer is:
wrong
'defective' is the definition.
(thesaurus)
'weight or conversely any number of grams' is the wordplay.
'weight' becomes 'w' (short for weight).
'conversely' says the letters should be written in reverse (in a converse direction).
'any number of' becomes 'n' (n can mean any number).
'grams' becomes 'g' (abbreviation).
'or' backwards is 'ro'.
'w'+'ro'+'n'+'g'='WRONG'
(Other definitions for wrong that I've seen before include "Unjust act" , "Erroneous" , "Injury - incorrect" , "Mistaken" , "Erronious" .)