foil 1 
(foil)
(foil)tr.v. foiled, foil·ing, foils
1. To prevent from being successful; thwart: The alarm system foiled the thieves' robbery attempt.
2. To obscure or confuse (a trail or scent) so as to evade pursuers.
n.
Archaic
Archaic
1. A repulse; a setback.
2. The trail or scent of an animal.
[Middle English foilen, to trample, defile, variant of filen, to defile; see FILE3.]