Source : Webster's Revised Unabridged Dictionary (1913)

Canto \Can"to\, n.; pl. {Cantos}. [It. canto, fr. L. cantus
   singing, song. See {Chant}.]
   1. One of the chief divisions of a long poem; a book.

   2. (Mus.) The highest vocal part; the air or melody in choral
      music; anciently the tenor, now the soprano.

   {Canto fermo}[It.] (Mus.), the plain ecclesiastical chant in
      cathedral service; the plain song.

Source : WordNet®

canto
     n 1: the highest part (usually the melody) in a piece of choral
          music
     2: a major division of a long poem