Definitions of foil:

• noun:   a light slender flexible sword tipped by a button
• noun:   a piece of thin and flexible sheet metal

  Example: "The photographic film was wrapped in foil"

• noun:   picture consisting of a positive photograph or drawing on a transparent base; viewed with a projector
• noun:   anything that serves by contrast to call attention to another thing's good qualities

  Example: "Pretty girls like plain friends as foils"

• noun:   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

  Example: "The fins of a fish act as hydrofoils"

• verb:   enhance by contrast

  Example: "In this picture, the figures are foiled against the background"

• verb:   cover or back with foil

  Example: "Foil mirrors"

• verb:   hinder or prevent (the efforts, plans, or desires) of

  Example: "Foil your opponent"

• name:  A surname (very rare: popularity rank in the U.S.: #26595)