Source : Webster's Revised Unabridged Dictionary (1913)

Harmonics \Har*mon"ics\, n.
   1. The doctrine or science of musical sounds.

   2. pl. (Mus.) Secondary and less distinct tones which
      accompany any principal, and apparently simple, tone, as
      the octave, the twelfth, the fifteenth, and the
      seventeenth. The name is also applied to the artificial
      tones produced by a string or column of air, when the
      impulse given to it suffices only to make a part of the
      string or column vibrate; overtones.

Source : WordNet®

harmonics
     n : the study of musical sound