foil2

noun

• 1metal hammered or rolled into a thin flexible sheet, used chiefly for covering or wrapping food:aluminum foil

• 2a person or thing that contrasts with and so emphasizes and enhances the qualities of another:the earthy taste of grilled vegetables is a perfect foil for the tart bite of creamy goat cheese
• a thin leaf of metal placed under a precious stone to increase its brilliance.

• 3 Architecture a leaf-shaped curve formed by the cusping of an arch or circle, typically occurring in groups of three or more in Gothic tracery.