or Cord, primarily denotes a slender rope or cordage. The word is formed of the Latin chorda, and that from the Greek χόρδη, a gut, of which strings may be made.

Geometry, a right line drawn from one part of an arc of a circle to another. Hence,

Chord of an Arc is a right line joining the extremities of that arc.

Music, the union of two or more sounds uttered at the same time, and forming together an entire harmony.

The natural harmony produced by the resonance of a sounding body, is composed of three different sounds, without reckoning their octaves, forming among themselves the most agreeable and perfect chord that can possibly be heard; for which reason they are called, on account of their excellence, perfect chords. Hence, in order to render the harmony complete, it is necessary that each chord should at least consist of three sounds. The trio is likewise found by musicians to include the perfection of harmony; either because in this all the chords, each in its full perfection, are used; or because, upon such occasions as render it improper to use them all, each in its integrity, arts have been successfully practised to deceive the ear, and to give it a contrary persuasion, by deluding it with the principal sounds of each chord, in such a manner as to render it forgetful of the other sounds necessary to their completion. Yet the octave of the principal sound produces new relations and new consonances, by the completion of the intervals; and hence, to have the assemblage of all the consonances in one and the same chord, this octave is commonly added. Moreover, as the addition of the dissonance produces a fourth sound superadded to the perfect chord, it becomes indispensably necessary, if we would render the chord full, to include a fourth part, in order to express this dissonance. Thus, the series of chords can neither be complete nor connected, but by means of four parts.

Chords are divided into perfect and imperfect. The perfect chord is that which we have just described, and which is composed of the fundamental sound below, of its third, its fifth, and its octave. Chords of this description are also subdivided into major and minor, according as the thirds which enter into their composition are flat or sharp. Some authors likewise give the name of perfect to all chords, even to dissonances, whose fundamental sounds are below. Imperfect chords are those in which the sixth instead of the fifth prevails, and in general all those whose lowest are not their fundamental sounds. These denominations, which were given before the fundamental bass was known, are now most unhappily applied; but those of chords direct and reversed are much more suitable in the same sense.

Chords are further divided into consonances and dissonances. The chords denominated consonances, are the perfect chord and its derivatives; every other chord is a dissonance. A table of both, according to the system of M. Rameau, may be seen in Rousseau's Musical Dictionary, vol. i. p. 27.