The Collaborative International Dictionary of English v.0.48:

Playhouse \Play"house`\, n. [AS. plegh[=u]s.]
   1. A building used for dramatic exhibitions; a theater.
      --Shak.
      [1913 Webster]

   2. A house for children to play in; a toyhouse.
      [1913 Webster]

WordNet (r) 3.0 (2006):

playhouse
    n 1: plaything consisting of a small model of a house that
         children can play inside of [syn: playhouse, wendy
         house]