Tet"ra*chord (?), n. [L. tetrachordon, Gr. , from four-stringed; (see Tetra-) + a chord: cf. F. t'etrachorde.] Anc. Mus.

A scale series of four sounds, of which the extremes, or first and last, constituted a fourth. These extremes were immutable; the two middle sounds were changeable.

© Webster 1913.