The Collaborative International Dictionary of English v.0.48:

Chasuble \Chas"u*ble\, n. [F. chasuble, LL. casubula, cassibula,
   casula, a hooded garment, covering the person like a little
   house; cf. It. casupola, casipola, cottage, dim of L. casa
   cottage.] (Eccl.)
   The outer vestment worn by the priest in saying Mass,
   consisting, in the Roman Catholic Church, of a broad, flat,
   back piece, and a narrower front piece, the two connected
   over the shoulders only. The back has usually a large cross,
   the front an upright bar or pillar, designed to be
   emblematical of Christ's sufferings. In the Greek Church the
   chasuble is a large round mantle. [Written also chasible,
   and chesible.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

chasuble
    n 1: a long sleeveless vestment worn by a priest when
         celebrating Mass