Look to exploit wretch (5)
I believe the answer is:
louse
'wretch' is the definition.
(thesaurus)
'look to exploit' is the wordplay.
'look' becomes 'lo' (archaic term meaning 'look!').
'to exploit' becomes 'use' (use is a kind of exploit).
'lo'+'use'='LOUSE'
(Other definitions for louse that I've seen before include "Rogue" , "Contemptible type" , "Common parasite on animals" , "Nit" , "Wingless parasite" .)