The Collaborative International Dictionary of English v.0.48:

Transubstantiate \Tran`sub*stan"ti*ate\, v. t. [LL.
   transubstantiatus, p. p. of transubstantiare to
   transubstantiate; L. trans across, over + substantia
   substance. See Substance.]
   1. To change into another substance. [R.]
      [1913 Webster]

            The spider love which transubstantiates all,
            And can convert manna to gall.        --Donne.
      [1913 Webster]

   2. (R. C. Theol.) To change, as the sacramental elements,
      bread and wine, into the flesh and blood of Christ.
      [1913 Webster]

WordNet (r) 3.0 (2006):

transubstantiate
    v 1: change (the Eucharist bread and wine) into the body and
         blood of Christ
    2: change or alter in form, appearance, or nature; "This
       experience transformed her completely"; "She transformed the
       clay into a beautiful sculpture"; "transubstantiate one
       element into another" [syn: transform, transmute,
       transubstantiate]