Disloyal type (3)
I believe the answer is:
rat
'disloyal type' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rat that I've seen before include "Long-tailed rodent" , "Despicable person" , "Tell-tale" , "Rodent; informer (colloq.)" , "one who deserts the sinking ship?" .)