n. [ LL. transubstantiatio: cf. F. transsubstantiation. ] 1. A change into another substance. [ 1913 Webster ]
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. [ 1913 Webster ]
(n) 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