The Collaborative International Dictionary of English v.0.48:

Shifting \Shift"ing\, a.
   1. Changing in place, position, or direction; varying;
      variable; fickle; as, shifting winds; shifting opinions or
      principles.
      [1913 Webster]

   2. Adapted or used for shifting anything.
      [1913 Webster]

   Shifting backstays (Naut.), temporary stays that have to be
      let go whenever the vessel tacks or jibes.

   Shifting ballast, ballast which may be moved from one side
      of a vessel to another as safety requires.

   Shifting center. See Metacenter.

   Shifting locomotive. See Switching engine, under
      Switch.
      [1913 Webster]