Blunt head shows futility (13)
I believe the answer is:
pointlessness
'futility' is the definition.
(I've seen this before)
'blunt head' is the wordplay.
'blunt' becomes 'pointless' (similar in meaning).
'head' becomes 'ness' (ness is a headland).
'pointless'+'ness'='POINTLESSNESS'
'shows' acts as a link.
(Other definitions for pointlessness that I've seen before include "that is demonstrated by blunt type" , "Futility" .)