Pointless to see reduction in common sense (4)
I believe the answer is:
nous
'common sense' is the definition.
(nous is a kind of common sense)
'pointless to see reduction' is the wordplay.
'pointless' becomes 'no use' (if something is no use it is pointless or futile).
'to see reduction' means to remove the last letter.
'nouse' with its final letter taken off is 'NOUS'.
'in' acts as a link.
(Other definitions for nous that I've seen before include "FT in Paris, say" , "How the French describe their own" , "Our (French); practical intelligence (colloq.)" , "French common sense" , "Gumption" .)