Scat! (4)
I believe the answer is:
shoo
'scat' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for shoo that I've seen before include "Push off" , "used to scare away animals" , "Exclamation used to chase away animals" , "Go away (interjection)" , "word of dismissal" .)