Source : Webster's Revised Unabridged Dictionary (1913)

Semitone \Sem"i*tone\, n. [Pref. semi- + tone. CF. {Hemitone}.]
   (Mus.)
   Half a tone; -- the name commonly applied to the smaller
   intervals of the diatonic scale.

   Note: There is an impropriety in the use of this word, and
         half step is now preferred. See {Tone}. --J. S. Dwight.

Source : WordNet®

semitone
     n : the musical interval between adjacent keys on a keyboard
         instrument [syn: {half step}]