The Collaborative International Dictionary of English v.0.48:

Hothouse \Hot"house`\, n.
   1. A house kept warm to shelter tender plants and shrubs from
      the cold air; a place in which the plants of warmer
      climates may be reared, and fruits ripened.
      [1913 Webster]

   2. A bagnio, or bathing house. [Obs.] --Shak.
      [1913 Webster]

   3. A brothel; a bagnio. [Obs.] --B. Jonson.
      [1913 Webster]

   4. (Pottery) A heated room for drying green ware.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hothouse
    n 1: a greenhouse in which plants are arranged in a pleasing
         manner [syn: conservatory, hothouse, indoor garden]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "hothouse":
   babied, cloche, coddled, cold frame, conservatory, coolhouse,
   dainty, delicate, forcing bed, forcing house, forcing pit, fragile,
   frail, glasshouse, greenhouse, hotbed, lathhouse, nursery,
   orangery, pampered, pinery, seedbed, sensitive, sheltered,
   shielded, spoiled, summerhouse