Source : Webster's Revised Unabridged Dictionary (1913)

Mezzo \Mez"zo\, a. [It., from L. medius middle, half. See {Mid},
   a.] (Mus.)
   Mean; not extreme.

Source : WordNet®

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