(Greek; " six strings ")
In music, a group of six tones in a specified pattern, specifically the interval pattern tone-tone-semitone-tone-tone (as in G-A-B-C-D-E).
The hexachord was apparently conceived in the 11th century when theorist Guido d'Arezzo noticed that the scales of the church mode s could be seen to overlap in their interval patterns. His system of solmization gave each hexachord the same syllables (ut-re-mi-fa-sol-la), and by means of overlapping hexachords the theorist could represent the complete "gamut" of pitches. Though counterintuitive to modern musicians, who think in terms of octaves, the concept of hexachords was fundamental to music theory throughout the Middle Ages and Renaissance.