Smile derisively (5)
I believe the answer is:
sneer
'smile derisively' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sneer that I've seen before include "Derisive remark" , "Contemptuous look" , "Contemptuous gesture" , "Contemptuous remark" , "Speak scornfully" .)