Fa
来自Big Physics
Middle English: representing (as an arbitrary name for the note) the first syllable of famuli, taken from a Latin hymn (see solmization).
wiktionary
From Latin famuli, from the first word of the fourth line of Ut queant laxis, the medieval hymn which solfège was based on because its lines started on each note of the scale successively.
etymonline
fa (n.)
fourth note in Guidonian scale; see gamut. Used from 13c. in Old French. It represents the first syllable in Latin famulus.
