The Collaborative International Dictionary of English v.0.48:

Ostensorium \Os`ten*so"ri*um\, Ostensory \Os*ten"so*ry\, n.; pl.
   L. -soria, E. -sories. [NL. ostensorium: cf. F.
   ostensoir. See Ostensible.] (R. C. Ch.)
   Same as Monstrance.
   [1913 Webster]