The Collaborative International Dictionary of English v.0.48:

Ciborium \Ci*bo"ri*um\, n.: pl. Ciboria. [LL., fr. L. ciborium
   a cup, fr. Gr. ? a seed vessel of the Egyptian bean; also, a
   cup made from its largeleaves, or resembling its seed vessel
   in shape.]
   1. (Arch.) A canopy usually standing free and supported on
      four columns, covering the high altar, or, very rarely, a
      secondary altar.
      [1913 Webster]

   2. (R. C. Ch.) The coffer or case in which the host is kept;
      the pyx.
      [1913 Webster]