La
Middle English: representing (as an arbitrary name for the note) the first syllable of Latin labii, taken from a Latin hymn (see solmization).
wiktionary
From Latin labii, from the first word of the sixth line of Ut queant laxis, the medieval hymn on which solfège was based because its lines started on each note of the scale successively.
Sound used to form meaningless song refrains. Of imitative origin. Compare Old English lā(a common exclamation), Ancient Greek λαλαγε(lalage, “babble”), German lallen(“to babble”).
From Middle English la, from Old English lā. More at lo.
Possibly a shortened form of lad.
etymonline
la (1)
musical note (sixth note of the diatonic scale), early 14c., see gamut. It represents the initial syllable of Latin labii "of the lips." In French and Italian it became the name of the musical note A, which is the sixth of the natural scale (C major).
la (2)
fem. form of the French definite article, used in English in certain phrases and sometimes added ironically to a woman's name with a suggestion of "prima donna" (OED examples begin 1860s). See le.
la (3)
Anglo-Saxon interjection of mild wonder or surprise, or grief; "oh, ah, indeed, verily."
