The Collaborative International Dictionary of English v.0.48:

Lazaret \Laz`a*ret"\ (l[a^]z`[.a]*r[e^]t"), Lazaretto
\Laz`a*ret"to\ (l[a^]z`[.a]*r[e^]t"t[-o]), n. [F. lazaret, or
   It. lazzeretto, fr. Lazarus. See Lazar.]
   1. A public building, hospital, or pesthouse for the
      reception of diseased persons, particularly those affected
      with contagious diseases.
      [1913 Webster]

   2. (Naut.)

   Note: (Pronounced by seamen l[a^]z`[.a]*r[=e]t") A low space
         under the after part of the main deck, used as a
         storeroom.
         [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

lazaret
    n 1: hospital for persons with infectious diseases (especially
         leprosy) [syn: lazaretto, lazaret, lazarette, lazar
         house, pesthouse]

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

LAZARET or LAZARETTO. A place selected by public authority, where vessels
coming from infected or unhealthy countries are required to perform
quarantine. Vide Health.