Unmannerly man (3)
I believe the answer is:
cad
'unmannerly man' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cad that I've seen before include "A knave, real rotter" , "designing software" , "Dishonourable man of decadent sort" , "A rotter, by Jove" , "Bounder, scoundrel" .)