Speak derisively (5)
I believe the answer is:
scoff
'speak derisively' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for scoff that I've seen before include "Speak derisively" , "Quickly swallow" , "Jeer - eat quickly" , "Deride - guzzle" , "Devour (informal)" .)