Parry a sword (4)
I believe the answer is:
foil
I believe this is a double definition.
'parry' is the first definition.
(I've seen this before)
'a sword' is the second definition.
(foil is a kind of sword)
(Other definitions for foil that I've seen before include "Check" , "hamper" , "Frustrate with fencing sword" , "Hinder - prevent" , "Frustrate; kitchen wrap" .)