Tĕt'ra-chōrd, n.

n. [Fr. tétrachorde, Lat. tetrachordon, Gr. τετράχορδον, from τετράχορδος, four-stringed, from τέτρα, for τέτορα, τέτταρα, τέσσαρα, from τέ-τορες, τέτταρες, τέσσαρες, four, and χορδή, a chord.] (Anc. Mus.) A 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.