The Collaborative International Dictionary of English v.0.48:

Mousing \Mous"ing\, n.
   1. The act of hunting mice.
      [1913 Webster]

   2. (Naut.) A turn or lashing of spun yarn or small stuff, or
      a metallic clasp or fastening, uniting the point and shank
      of a hook to prevent its unhooking or straighening out.
      [1913 Webster]

   3. A ratchet movement in a loom.
      [1913 Webster]

   Mousing hook, a hook with an attachment which prevents its
      unhooking.
      [1913 Webster]