Source : Webster's Revised Unabridged Dictionary (1913)

Solo \So"lo\, n.; pl. E. {Solos}, It. {Soli}. [It., from L.
   solus alone. See {Sole}, a.] (Mus.)
   A tune, air, strain, or a whole piece, played by a single
   person on an instrument, or sung by a single voice.