Source : Webster's Revised Unabridged Dictionary (1913)

Mezzo-soprano \Mez"zo-so*pra"no\, a. (Mus.)
   Having a medium compass between the soprano and contralto; --
   said of the voice of a female singer. -- n.
   (a) A mezzo-soprano voice.
   (b) A person having such a voice.

Source : WordNet®

mezzo-soprano
     n 1: a soprano with a voice between soprano and contralto [syn: {mezzo}]
     2: the female singing voice between contralto and soprano [syn:
         {mezzo}]