Riposte; laboratory vessel (6)
I believe the answer is:
retort
This clue is a double definition.
'riposte' is the first definition.
(I know that riposte can be written as retort)
'laboratory vessel' is the second definition.
(I've seen this in another clue)
(Other definitions for retort that I've seen before include "Chem. flask; sharp answer" , "A sharp reply or vessel used in distilling" , "Sharp response; lab item" , "Riposte, reply" , "Still" .)