to whistle off

Whistle \Whis"tle\, v. t.
   [1913 Webster]
   1. To form, utter, or modulate by whistling; as, to whistle a
      tune or an air.
      [1913 Webster]

   2. To send, signal, or call by a whistle.
      [1913 Webster]

            He chanced to miss his dog; we stood still till he
            had whistled him up.                  --Addison.
      [1913 Webster]

   {To whistle off}.
      (a) To dismiss by a whistle; -- a term in hawking. "AS a
          long-winged hawk when he is first whistled off the
          fist, mounts aloft." --Burton.
      (b) Hence, in general, to turn loose; to abandon; to
          dismiss.
          [1913 Webster]

                I 'ld whistle her off, and let her down the wind
                To prey at fortune.               --Shak.
          [1913 Webster]

   Note: "A hawk seems to have been usually sent off in this
         way, against the wind when sent in search of prey; with
         or down the wind, when turned loose, and abandoned."
         --Nares.
         [1913 Webster]