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1.                 From The Collaborative International Dictionary of English v.0.48:
                   
   
   
                   
                     
   Tasto \Tas"to\ (t[aum]s"t[-o]), n. [It.] (Mus.)
      A key or thing touched to produce a tone.
      [1913 Webster]
      Tasto solo, single touch; -- in old music, a direction
         denoting that the notes in the bass over or under which it
         is written should be performed alone, or with no other
         chords than unisons and octaves.
         [1913 Webster]