Source : Webster's Revised Unabridged Dictionary (1913)

Melody \Mel"o*dy\, n.; pl. {Melodies}. [OE. melodie, F.
   m['e]lodie, L. melodia, fr. Gr. ? a singing, choral song, fr.
   ? musical, melodious; ? song, tune + ? song. See {Ode}.]
   1. A sweet or agreeable succession of sounds.

            Lulled with sound of sweetest melody. --Shak.

   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.

   Note: 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.

   3. The air or tune of a musical piece.

   Syn: See {Harmony}.

Source : WordNet®

melody
     n 1: a succession of notes forming a distinctive sequence; "she
          was humming an air from Beethoven" [syn: {tune}, {air},
          {strain}, {melodic line}, {line}, {melodic phrase}]
     2: the perception of pleasant arrangements of musical notes
        [syn: {tonal pattern}]