Heptachord

Hep"ta*chord (?), n. [Gr. "epta`xordos seven-stringed; "epta` seven + xordh` chord: cf. F. heptacorde. See Seven, and Chord.] 1. (Anc. Mus.) (a) A system of seven sounds. (b) A lyre with seven chords.

2. (Anc. Poet.) A composition sung to the sound of seven chords or tones. Moore (Encyc. of Music).