Derisory, preposterous (6)
I believe the answer is:
absurd
This clue is a double definition.
'derisory' is the first definition.
(I know that derisory can be written as absurd)
'preposterous' is the second definition.
(synonyms)
(Other definitions for absurd that I've seen before include "Quite ridiculous, laughable" , "Ludicrous, silly" , "Ridiculous, ludicrous" , "Patently ridiculous" , "'Ridiculous, silly (6)'" .)