foil1
  
  v.
  - prevent the success of.
 - Hunting  (of a hunted animal) cross (a scent or track) in such a way as to confuse the hounds.
 
n.
  - Hunting  the track or scent of a hunted animal.
 - archaic a setback or defeat.
 
 
  Etymology
  ME (in the sense ‘trample down’): perh. from OFr. fouler ‘to full cloth, trample’, based on L. fullo ‘fuller’.
 
  
    
foil2
  
  n.
   - metal hammered or rolled into a thin flexible sheet. 
▸a thin leaf of metal placed under a precious stone to increase its brilliance.
 - a person or thing that contrasts with and so enhances the qualities of another.
 - Architecture  a leaf-shaped curve formed by the cusping of an arch or circle.
 
 
  Etymology
  ME: via OFr. from L. folium ‘leaf’.
 
  
    
foil3
  
  n.
 a light, blunt-edged fencing sword with a button on its point.
 
  Derivative
  
  Etymology
  C16: of unknown origin.
 
  
    
foil4
  
  n.
 each of the structures fitted to a hydrofoil's hull to lift it clear of the water at speed.