Guido d'Arezzo (or Guido of Arezzo), commonly refered to as the father of modern music, was a Benedictine monk and a musician who lived in the 11th century. Druing his lifetime, Guido developed the six-note scale for reading music — the "hexachord" system.

The names of the first six notes of the scale, ut, re, mi, fa, sol, and la, are taken from the first syllables of six lines of a hymn addressed to St. John the Baptist: "Ut queant laxis resonare fibris Mira gestorum famuli tuorum, Solve polluti labii reatum, Sancte Iohannes."

Now to the word gamut. It is merely a contraction of "gamma," which represented the last note on Guido d'Arezzo's musical scale, and "ut," which represented the first note used in his singing scale. Gamut came to mean the whole range of notes possessed by an instrument or voice, and over time it has developed further to mean the entire scale of most anything.