Common sense to impugn outrageously (8)
I believe the answer is:
gumption
'common sense' is the definition.
(I know that common sense can be written as gumption)
'to impugn outrageously' is the wordplay.
'outrageously' is an anagram indicator.
'to'+'impugn'='toimpugn'
'toimpugn' is an anagram of 'GUMPTION'.
(Other definitions for gumption that I've seen before include "Informal common sense or initiative" , "Courage needed!" , "Fortitude and determination" , "Informal drive and initiative" , "To impugn (anag) - common sense" .)