Unethical one (5)
I believe the answer is:
louse
'unethical one' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for louse that I've seen before include "Contemptible type" , "Bloodsucking parasitic insect" , "Common parasite on animals" , "Rogue" , "Wingless parasite" .)