Hexachord

In music, a hexachord (also hexachordon) is a six-note series, as exhibited in a scale (hexatonic or hexad) or tone row.

The term was adopted in this sense during the Middle Ages and adapted in the 20th century in Milton Babbitt's serial theory.

These six names are derived from the first syllable of each half-verse of the first stanza of the 8th-century Vesper hymn Ut queant laxis resonare fibris / Mira gestorum famuli tuorum, etc.

Starting in the 14th century, these three hexachords were extended in order to accommodate the increasing use of signed accidentals on other notes.

[7] Allen Forte in The Structure of Atonal Music[9] redefines the term hexachord to mean what other theorists (notably Howard Hanson in his Harmonic Materials of Modern Music: Resources of the Tempered Scale[10]) mean by the term hexad, a six-note pitch collection which is not necessarily a contiguous segment of a scale or a tone row.