Origin: 1350–1400; Middle English foille, foil < Old French fuelle, fueille, foille (< Latin folia leaves), fuel, fueil, foil (< Latin folium leaf, blade)
"thin sheet of metal," late 14c., from O.Fr. fueille "leaf," from L. folia "leaves," pl. (mistaken for fem. sing.) of folium "leaf" (see folio). The sense of "one who enhances another by contrast" (1580s) is from the practice of backing a gem with metal foil to make it shine
better. The meaning "light sword used in fencing" (1590s) could be from this sense, or from foil (v.). The modern sense of "metallic food wrap" is from 1946.