Mock, sneer at (6)
I believe the answer is:
deride
This clue is a double definition.
'mock' is the first definition.
(deriding is a kind of mocking)
'sneer at' is the second definition.
(I've seen this in another clue)
(Other definitions for deride that I've seen before include "Mock, scorn" , "Jeer, belittle" , "Express contempt for" , "Disparage" , "Mock and jeer" .)