Look slyly (4)
I believe the answer is:
leer
'look slyly' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for leer that I've seen before include "Suggestive or sneering grin" , "Look suggestively" , "Ogle, smirk" , "Stare suggestively" , "Lascivious gaze" .)