The Collaborative International Dictionary of English v.0.48:

Cuirass \Cui*rass"\ (kw[-e]*r[.a]s", or kw[=e]"r[a^]s; 277), n.;
   pl. Cuirasses(-[e^]z). [F.cuirasse, orig., a breastplate of
   leather, for OF. cuir['e]e, cuirie influenced by It. corazza,
   or Sp. coraza, fr. an assumed LL. coriacea, fr. L. coriaceus,
   adj., of leather, fr. corium leather, hide; akin to Gr.
   cho`rion intestinal membrane, OSlav. skora hide, Lith. skura
   hide, leather. Cf. Coriaceous.]
   1.
      (a) A piece of defensive armor, covering the body from the
          neck to the girdle.
      (b) The breastplate taken by itself.
          [1913 Webster]

   Note: The cuirass covered the body before and behind. It
         consisted of two parts, a breast- and backpiece of iron
         fastened together by means of straps and buckles or
         other like contrivances. It was originally, as the name
         imports, made of leather, but afterward of metal.
         --Grose.
         [1913 Webster]

   2. (Zool) An armor of bony plates, somewhat resembling a
      cuirass.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cuirass
    n 1: medieval body armor that covers the chest and back