foil in WordNet English dictionary

1. hinder or prevent (the efforts, plans, or desires) of
   "What ultimately frustrated every challenger was Ruth's amazing September surge"; "foil your opponent"
   thwart  queer  spoil  scotch  foil  cross  frustrate  baffle  bilk 
   
2. cover or back with foil
   "foil mirrors"
   foil 
   
3. enhance by contrast
   "In this picture, the figures are foiled against the background"
   foil 
   

1. anything that serves by contrast to call attention to another thing's good qualities
   "pretty girls like plain friends as foils"
   foil  enhancer 
   
2. a light slender flexible sword tipped by a button
   foil 
   
3. a piece of thin and flexible sheet metal
   "the photographic film was wrapped in foil"
   foil 
   
4. picture consisting of a positive photograph or drawing on a transparent base; viewed with a projector
   foil  transparency 
   
5. a device consisting of a flat or curved piece (as a metal plate) so that its surface reacts to the water it is passing through
   "the fins of a fish act as hydrofoils"
   hydrofoil  foil