The Collaborative International Dictionary of English v.0.48:

Sanatorium \San`a*to"ri*um\, n. [NL. See Sanatory.]
   An establishment for the treatment of the sick; a resort for
   invalids. See Sanitarium.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sanatorium
    n 1: a hospital for recuperation or for the treatment of chronic
         diseases [syn: sanatorium, sanatarium, sanitarium]
    2: pejorative terms for an insane asylum [syn: Bedlam, booby
       hatch, crazy house, cuckoo's nest, funny farm, funny
       house, loony bin, madhouse, nut house, nuthouse,
       sanatorium, snake pit]