Frustrate, thwart (4)
I believe this clue is a double definition.
'frustrate' is the first definition.
(I've seen this before)
'thwart' is the second definition.
(I've seen this before)
(Other definitions for stymie that I've seen before include "Block or obstruct as in golf (6)" , "Block or thwart, perhaps in golf" , "Situation from which it is almost impossible to proceed" , "Thwart -- my ties (anag)" , "'Hinder, prevent progress (6)'" .)
I believe this is a double definition.
'frustrate' is the first definition.
(I know that frustrate can be written as foil)
'thwart' is the second definition.
(I know that thwart can be written as foil)
(Other definitions for foil that I've seen before include "Repulse" , "Frustrate - sheet - rapier" , "Frustrate with fencing sword" , "Thin metal - sword" , "Prevent from succeeding" .)