The Collaborative International Dictionary of English v.0.48:

Consubstantial \Con`sub*stan"tial\, a. [L. consubstantialis;
   con- + substantialis: cf. F. consubstantiel. See
   Substantial.]
   Of the same kind or nature; having the same substance or
   essence; coessential.
   [1913 Webster]

         Christ Jesus . . . coeternal and consubstantial with
         the Father and with the Holy Ghost.      --Foxe.
   [1913 Webster]

WordNet (r) 3.0 (2006):

consubstantial
    adj 1: regarded as the same in substance or essence (as of the
           three persons of the Trinity)