Sly glance (4)
I believe the answer is:
leer
'sly glance' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for leer that I've seen before include "Give lascivious look" , "Look lasciviously at" , "Look lecherously" , "Suggestive or sneering look" , "Lewd look" .)