Look furtively (4)
I believe the answer is:
peep
'look furtively' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for peep that I've seen before include "Look slyly" , "Chirp" , "Sly look (palindrome)" , "Peek" , "Look furtively (either way)" .)