ETYM Old Eng. foil leaf, Old Fren. foil, fuil, fueil, foille, fueille, French feuille, from Latin folium, pl. folia.
1. A light slender flexible sword tipped by a button.
2. A positive photograph or drawing on a transparent base; viewed with a projector; SYN. transparency.
3. A very thin and flexible sheet of metal.