Meaning

noun a piece of thin and flexible sheet metal

noun anything that serves by contrast to call attention to another thing's good qualities

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

originFrom Middle English foyle, from Middle French fueille, from Old French fueille (“plant leaf”), from Late Latin folia, the plural of folium, mistaken as a singular feminine. The literary sense is from the practice of backing a gem with metal foil to make it shine more brilliantly. Doublet of folio and folium, distantly also with phyllo and phyllon.

Etymology from Wiktionary, CC BY-SA 3.0