Source : Webster's Revised Unabridged Dictionary (1913)

Transubstantiation \Tran`sub*stan`ti*a"tion\, n. [LL.
   transubstantiatio: cf. F. transsubstantiation.]
   1. A change into another substance.

   2. (R. C. Theol.) The doctrine held by Roman Catholics, that
      the bread and wine in the Mass is converted into the body
      and blood of Christ; -- distinguished from
      consubstantiation, and impanation.

Source : WordNet®

transubstantiation
     n 1: the Roman Catholic doctrine that the whole substance of the
          bread and the wine changes into the substance of the
          body and blood of Christ when consecrated in the
          Eucharist
     2: an act that changes the form or character or substance of
        something [syn: {transmutation}]