Meaning

noun a complete extent or range:

noun the entire scale of musical notes

origin1520s, original sense “lowest note of musical scale”, contraction of Medieval Latin gamma ut, from gamma (“Greek letter, corresponding to the musical note G”) + ut (“first solfège syllable, now replaced by do”). In modern terms, “G do” – the first note of the G scale. Meaning later extended to mean all the notes of a scale, and then more generally any complete range.

Etymology from Wiktionary, CC BY-SA 3.0