Melody

n. pl. Melodies (#).
  1. A sweet or agreeable succession of sounds.
  2. (Mus.) A rhythmical succession of single tones, ranging for the most part within a given key, and so related together as to form a musical whole, having the unity of what is technically called a musical thought, at once pleasing to the ear and characteristic in expression.
  3. The air or tune of a musical piece.

Melody consists in a succession of single tones; harmony is a consonance or agreement of tones, also a succession of consonant musical combinations or chords.