la (1) Look up la at Dictionary.com
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) Look up la at Dictionary.com
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).
la (3) Look up la at Dictionary.com
Anglo-Saxon interjection of mild wonder or surprise, or grief; "oh, ah, indeed, verily."