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]