The Collaborative International Dictionary of English v.0.48:

Horse \Horse\ (h[^o]rs), v. t. [imp. & p. p. Horsed; p. pr. &
   vb. n. Horsing.] [AS. horsion.]
   1. To provide with a horse, or with horses; to mount on, or
      as on, a horse. "Being better horsed, outrode me." --Shak.
      [1913 Webster]

   2. To sit astride of; to bestride. --Shak.
      [1913 Webster]

   3. To mate with (a mare); -- said of the male.
      [1913 Webster]

   4. To take or carry on the back; as, the keeper, horsing a
      deer. --S. Butler.
      [1913 Webster]

   5. To place on the back of another, or on a wooden horse,
      etc., to be flogged; to subject to such punishment.
      [1913 Webster]