melody n.

c. 1300, melodie, "vocal or instrumental music, a succession of agreeable musical sounds," from Old French melodie "music, song, tune" (12c.) and directly from Late Latin melodia "a pleasant song" (in Medieval Latin also "music" generally), from Greek melōidia "a singing, a chanting; a choral song, a tune for lyric poetry," from melos "song, part of song; limb, member" (a word of uncertain origin) + ōidē "song, ode" (see ode). From late 14c. as "a song of clear and balanced form." Sense of "a series of tones so related to one another as to produce a distinct musical phrase or idea, a tune" is by c. 1600. Meaning "the principal voice-part in a harmonic composition" is by 1880.