Expression to chase away an animal (4)
I believe the answer is:
shoo
'expression to chase away an animal' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for shoo that I've seen before include "told to go away!" , "Drive away" , "Get away" , "Sling your hook!" , "Exclamation used to chase away animals" .)