sol-fa: [16] Sol-fa is a lexicalization of two of the syllables (sol and fa) used in the tonic sol-fa system for representing the notes of the musical scale. In Italian the combination was turned into a verb, solfeggiare, a derivative of which has given English solfeggio ‘use of the sol-fa system’ [18]. (Another English word based on the name of notes of the scale is gamut.)
"syllables used in solmization taken collectively," 1540s, from Italian, from Medieval Latin sol and fa, two notes of the musical scale (see gamut). As a verb from 1560s; compare solfeggio "use the sol-fa system" (1774), from Italian solfeggiare.
