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]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "sanatorium":
   VA hospital, asylum, base hospital, clinic, community hospital,
   convalescent home, convalescent hospital, evacuation hospital,
   field hospital, general hospital, home, hospital, infirmary,
   inpatient clinic, maison de sante, mental hospital, nursing home,
   osteopathic hospital, outpatient clinic, policlinic, polyclinic,
   private hospital, proprietary hospital, public hospital, rest home,
   sanitarium, sick bay, sickbed, sickroom, special hospital,
   station hospital, surgical hospital, teaching hospital,
   veterans hospital, voluntary hospital, ward, well-baby clinic