Difficult second argument (5)
I believe the answer is:
stiff
'difficult' is the definition.
(I've seen this before)
'second argument' is the wordplay.
'second' becomes 's' (common abbreviation).
'argument' becomes 'tiff' (I've seen this before).
's'+'tiff'='STIFF'
(Other definitions for stiff that I've seen before include "Unyielding" , "Rigid, unbending" , "Formal" , "Awkward" , "Unfriendly" .)