The Collaborative International Dictionary of English v.0.48:

Corselet \Corse"let\ (k?rs"l?t), n. [F., dim. of OF. cors. F.
   corps, body. See Corse.]
   1. Armor for the body, as, the body breastplate and backpiece
      taken together; -- also, used for the entire suit of the
      day, including breastplate and backpiece, tasset and
      headpiece.
      [1913 Webster]

   2. (Zool.) The thorax of an insect.
      [1913 Webster]

WordNet (r) 3.0 (2006):

corselet
    n 1: a piece of body armor for the trunk; usually consists of a
         breastplate and back piece [syn: corselet, corslet]