From The Food Encyclopedia by Jacques Rolland and Carol Sherman
Also filet. From the French filet, a diminutive of fil, meaning "thread", fillet is the term for a boneless strip or piece of meat or fish. Fillet is the style both for the verb and the noun. In fish terms, a single fillet is one side of the fish; a double fillet, also called a butterfly fillet, is both sides of the fish, with a small piece of the flesh and the belly skin holding them together on one side.
