Hostile dog (3)
I believe the answer is:
cur
'hostile dog' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cur that I've seen before include "Mongrel - coward" , "Vicious dog" , "Mongrel - cowardly person" , "Non-pedigree dog" , "Useless dog" .)