The Collaborative International Dictionary of English v.0.48:

Workhouse \Work"house`\, n.; pl. Workhouses. [AS.
   weorch[=u]s.]
   [1913 Webster]
   1. A house where any manufacture is carried on; a workshop.
      [1913 Webster]

   2. A house in which idle and vicious persons are confined to
      labor.
      [1913 Webster]

   3. A house where the town poor are maintained at public
      expense, and provided with labor; a poorhouse.
      [1913 Webster]