The Collaborative International Dictionary of English v.0.48:

Basso \Bas"so\, n. [It., fr. LL. bassus. See Base, a.] (Mus.)
      (a) The bass or lowest part; as, to sing basso.
      (b) One who sings the lowest part.
      (c) The double bass, or contrabasso.
          [1913 Webster]

   Basso continuo. [It., bass continued.] (Mus.) A bass part
      written out continuously, while the other parts of the
      harmony are indicated by figures attached to the bass;
      continued bass.
      [1913 Webster]

WordNet (r) 3.0 (2006):

basso
    n 1: an adult male singer with the lowest voice [syn: bass,
         basso]
    2: the lowest adult male singing voice [syn: bass, bass
       voice, basso]