Mangy mutt (3)
I believe the answer is:
cur
'mangy mutt' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cur that I've seen before include "Vicious dog" , "Mangy dog" , "Useless dog" , "A low worthless dog" , "Mongrel - cowardly person" .)