The Collaborative International Dictionary of English v.0.48:

Asylum \A*sy"lum\, n.; pl. E. Asylums, L. Asyla. [L. asylum,
   Gr. ?, fr. ? exempt from spoliation, inviolable; 'a priv. + ?
   right of seizure.]
   1. A sanctuary or place of refuge and protection, where
      criminals and debtors found shelter, and from which they
      could not be forcibly taken without sacrilege.
      [1913 Webster]

            So sacred was the church to some, that it had the
            right of an asylum or sanctuary.      --Ayliffe.
      [1913 Webster]

   Note: The name was anciently given to temples, altars,
         statues of the gods, and the like. In later times
         Christian churches were regarded as asylums in the same
         sense.
         [1913 Webster]

   2. Any place of retreat and security.
      [1913 Webster]

            Earth has no other asylum for them than its own cold
            bosom.                                --Southey.
      [1913 Webster]

   3. An institution for the protection or relief of some class
      of destitute, unfortunate, or afflicted persons; as, an
      asylum for the aged, for the blind, or for the insane; a
      lunatic asylum; an orphan asylum.
      [1913 Webster]

WordNet (r) 3.0 (2006):

asylum
    n 1: a shelter from danger or hardship [syn: refuge,
         sanctuary, asylum]
    2: a hospital for mentally incompetent or unbalanced person
       [syn: mental hospital, psychiatric hospital, mental
       institution, institution, mental home, insane asylum,
       asylum]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "asylum":
   VA hospital, almshouse, base hospital, bedlam, bird sanctuary,
   bolt-hole, bughouse, cache, clinic, community hospital,
   concealment, convalescent home, convalescent hospital, corner,
   cover, covert, coverture, cranny, crazy house, cubby, cubbyhole,
   dark corner, den, dugout, evacuation hospital, farm,
   field hospital, forest preserve, foster home, foxhole, funk hole,
   game preserve, game sanctuary, general hospital, halfway house,
   harbor, harbor of refuge, harborage, haven, hideaway, hideout,
   hidey hole, hiding, hiding place, hole, home, hospice, hospital,
   hospitium, infirmary, inpatient clinic, insane asylum, institution,
   inviolability, lair, lunatic asylum, madhouse, maison de sante,
   mental home, mental hospital, mental institution, niche, nook,
   nursing home, nuthouse, orphanage, osteopathic hospital,
   outpatient clinic, padded cell, policlinic, polyclinic, poor farm,
   poorhouse, port, preserve, private hospital, proprietary hospital,
   psychiatric ward, psychopathic hospital, public hospital, recess,
   refuge, rest home, retreat, safe haven, safehold, sanatorium,
   sanctuary, secret place, security, shelter, sick bay, sickbed,
   sickroom, snug harbor, special hospital, stash, state hospital,
   station hospital, stronghold, surgical hospital, teaching hospital,
   undercovert, veterans hospital, voluntary hospital, ward,
   well-baby clinic, workhouse



Bouvier's Law Dictionary, Revised 6th Ed (1856):

ASYLUM. A place, of refuge where debtors and criminals fled for safety.
     2. At one time, in Europe, churches and other consecrated places served
as asylums, to the disgrace of the law. These never protected criminals in
the United States. It may be questioned whether the house of an ambassador
(q.v.) would not afford protection temporarily, to a person who should take
refuge there.