The Collaborative International Dictionary of English v.0.48:

Infirmary \In*firm"a*ry\ ([i^]n*f[~e]rm"[.a]*r[y^]), n.; pl.
   Infirmaries (-r[i^]z). [Cf. OE. fermerie, OF. enfermerie,
   F. infirmerie, LL. infirmaria. See Infirm.]
   A hospital, or place where the infirm or sick are lodged and
   nursed gratuitously, or where out-patients are treated.
   [1913 Webster]

WordNet (r) 3.0 (2006):

infirmary
    n 1: a health facility where patients receive treatment [syn:
         hospital, infirmary]

Moby Thesaurus II by Grady Ward, 1.0:

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