Foil (6)
(Other definitions for stymie that I've seen before include "Obstruction (originally at golf)" , "'Hinder, prevent progress (6)'" , "Thwart, foil" , "Block or thwart, as on golf course" , "Old putting problem" .)
'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 "Hinder or prevent" , "check" , "Oppose successfully" , "Frustrate, prevent from doing" , "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 "Fighting blade" , "Foil for riposte" , "Fencing blade" , "Type of sword" , "It may offer riposte" .)