Foil (6)
'foil' is the definition.
(I know that foil can be written as thwart)
This is all the clue.
(Other definitions for thwart that I've seen before include "Oppose successfully" , "Defeat" , "Hinder or prevent" , "Frustrate or foil" , "seat for oarsman" .)
'foil' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for epee that I've seen before include "piece of fencing" , "Pointed weapon" , "Fencing sword, heavier than a foil" , "Olympic event" , "Bit of fencing" .)