KEY (in O. Eng. caég; the ultimate origin of the word is unknown; it appears only in Old Frisian kei of other Teutonic languages; until the end of the 17th century the pronunciation was kay, as in other words in O. Eng. ending in aég; cf. daég, day; claég, clay; the New English Dictionary takes the change to kee to be due to northern influence), an instrument of metal used for the opening and closing of a lock (see Lock). Until the 14th century bronze and not iron was most commonly used. The terminals of the stem of the keys were frequently decorated, the “bow” or loop taking the form sometimes of a trefoil, with figures inscribed within it; this decoration increased in the 16th century, the terminals being made in the shape of animals and other figures. Still more elaborate ceremonial keys were used by court officials; a series of chamberlains’ keys used during the 18th and 19th centuries in several courts in Europe is in the British Museum. The terminals are decorated with crowns, royal monograms and ciphers. The word “key” is by analogy applied to things regarded as means for the opening or closing of anything, for the making clear that which is hidden. Thus it is used of an interpretation as to the arrangement of the letters or words of a cipher, of a solution of mathematical or other problems, or of a translation of exercises or books, &c., from a foreign language. The term is also used figuratively of a place of commanding strategic position. Thus Gibraltar, the “Key of the Mediterranean,” was granted in 1462 by Henry IV. of Castile, the arms, gules, a castle proper, with key pendant to the gate, or; these arms form the badge of the 50th regiment of foot (now 2nd Batt. Essex Regiment) in the British army, in memory of the part which it took in the siege of 1782. The word is also frequently applied to many mechanical contrivances for unfastening or loosening a valve, nut, bolt, &c., such as a spanner or wrench, and to the instruments used in tuning a pianoforte or harp or in winding clocks or watches. A farther extension of the word is to appliances or devices which serve to lock or fasten together distinct parts of a structure, as the “key-stone” of an arch, the wedge or piece of wood, metal, &c., which fixes a joint, or a small metal instrument, shaped like a U, used to secure the bands in the process of sewing in bookbinding.

In musical instruments the term “key” is applied in certain wind instruments, particularly of the wood-wind type, to the levers which open and close valves in order to produce various notes, and in keyboard instruments, such as the organ or the pianoforte, to the exterior white or black parts of the levers which either open or shut the valves to admit the wind from the bellows to the pipes or to release the hammers against the strings (see Keyboard). It is from this application of the word to these levers in musical instruments that the term is also used of the parts pressed by the finger in typewriters and in telegraphic instruments.

A key is the insignia of the office of chamberlain in a royal household (see Chamberlain and Lord Chamberlain). The “power of the keys” (clavium potestas) in ecclesiastical usage represents the authority given by Christ to Peter by the words, “I will give unto thee the keys of the kingdom of heaven” (Matt. xvi. 19). This is claimed by the Roman Church to have been transmitted to the popes as the successors of St Peter.

“Key” was formerly the common spelling of “quay,” a wharf, and is still found in America for “cay,” an island reef or sandbank off the coast of Florida (see Quay).

The origin of the name Keys or House of Keys, the lower branch of the legislature, the court of Tynwald, of the Isle of Man, has been much discussed, but it is generally accepted that it is a particular application of the word “key” by English- and not Manx-speaking people. According to A. W. Moore, History of the Isle of Man, i. 160 sqq. (1900), in the Manx statutes and records the name of the house was in 1417 Claves Manniae et Claves legis, Keys of Man and Keys of the Law; but the popular and also the documentary name till 1585 seems to have been “the 24,” in Manx Kiare as feed. From 1585 to 1734 the name was in the statutes, &c., “the 24 Keys,” or simply “the Keys.” Moore suggests that the name was possibly originally due to an English “clerk of the rolls,” the members of the house being called in to “unlock or solve the difficulties of the law.” There is no evidence for the suggestion that Keys is an English corruption of Kiare-as, the first part of Kiare as feed. Another suggestion is that it is from a Scandinavian word keise, chosen.