The Collaborative International Dictionary of English v.0.48:

Sitfast \Sit"fast`\, a. [Sit + fast.]
   Fixed; stationary; immovable. [R.]
   [1913 Webster]

         'T is good, when you have crossed the sea and back,
         To find the sitfast acres where you left them.
                                                  --Emerson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sitfast \Sit"fast`\, n. (Far.)
   A callosity with inflamed edges, on the back of a horse,
   under the saddle.
   [1913 Webster]