E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Gam’mut, or Gamut (g hard).
It is gamma ut, “ut” being the first word in the Guido-von-Arrezzo scale of ut, re, mi, fa, sol, la. In the eleventh century the ancient scale was extended a note below the Greek proslamban’omy note (our A), the first space of the bass staff. The new note was termed (gamma), and when “ut” was substituted by Arrezzo the “supernumerary” note was called gamma or ut, or shortly gamm’ ut—i.e.“Gut.” The gammut, therefore, properly means the diatonic scale beginning in the bass clef with “G.”
(gamma), and when “ut” was substituted by Arrezzo the “supernumerary” note was called gamma or ut, or shortly gamm’ ut—i.e. 
