Sassy (4)
I believe the answer is:
pert
'sassy' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pert that I've seen before include "Impudent, cheeky" , "Saucy and chipper" , "Jaunty" , "Cheeky, saucy" , "Saucy, maybe brash" .)