Foil. 1. (Through O. Fr. from Lat. folium, a leaf, modern Fr. feuille), a leaf, and so used in heraldry and in plant names, such as the “trefoil” clover; and hence applied to anything resembling a leaf. In architecture, the word appears for the small leaf-like spaces formed by the cusps of tracery in windows or panels, and known, according to the number of such spaces, as “quatrefoil,” “cinquefoil,” &c. The word is also found in “counterfoil,” a leaf of a receipt or cheque book, containing memoranda or a duplicate of the receipt or draft, kept by the receiver or drawer as a “counter” or check. “Foil” is particularly used of thin plates of metal, resembling a leaf, not in shape as much as in thinness. In thickness foil comes between “leaf” and “sheet” metal. In jewelry, a foil of silvered sheet copper, sometimes known as Dutch foil, is used as a backing for paste gems, or stones of inferior lustre or colour. This is coated with a mixture of isinglass and translucent colour, varying with the stones to be backed, or, if only brilliancy is required, left uncoloured, but highly polished. From this use of “foil,” the word comes to mean, in a figurative sense, something which by contrast, or by its own brightness, serves to heighten the attractive qualities of something else placed in juxtaposition. The commonest “foil” is that generally known as “tinfoil.” The ordinary commercial “tinfoil” usually consists chiefly of lead, and is used for the wrapping of chocolate or other sweetmeats, tobacco or cigarettes. A Japanese variegated foil gives the effect of “damaskeening.” A large number of thin plates of various metals, gold, silver, copper, together with alloys of different metals are soldered together in a particular order, a pattern is hammered into the soldered edges, and the whole is hammered or rolled into a single thin plate, the pattern then appearing in the order in which the various metals were placed.
2. (From an O. Fr. fuler or foler, modern fouler, to tread or trample, to “full” cloth, Lat. fullo, a fuller), an old hunting term, used of the running back of an animal over its own tracks, to confuse the scent and baffle the hounds. It is also used in wrestling, of a “throw.” Thus comes the common use of the word, in a figurative sense, with reference to both these meanings, of baffling or defeating an adversary, or of parrying an attack.
3. As the name of the weapon used in fencing (see Foil-Fencing) the word is of doubtful origin. One suggestion, based on a supposed similar use of Fr. fleuret, literally a “little flower,” for the weapon, is that foil means a leaf, and must be referred in origin to Lat. folium. A second suggestion is that it means “blunted,” and is the same as (2). A third is that it is an adaptation of an expression “at foils,” i.e. “parrying.” Of these suggestions, according to the New English Dictionary, the first has nothing to support it, the second is not supported by any evidence that in sense (2) the word ever meant to blunt. The third has some support. Finally a suggestion is made that the word is an alteration of an old word “foin,” meaning a thrust with a pointed weapon. The origin of this word is probably an O. Fr. foisne, from the Lat. fuscina, a three-pronged fork.
