A thin sheet of metal, or a fencing weapon
Foil (metal), a quite thin sheet 
of metal, usually manufactured with a rolling ... a printmaking technique; Foil (
fencing), one of the three weapons used in modern fencing; Foil (literature), a 
subsidiary... [DOC] [TLE] Foil | Word Foil at Open Dictionary of English by LearnThat Foundation [PAR] The art or sport of fencing with such a sword.