The Collaborative International Dictionary of English v.0.48:

Coessential \Co`es*sen"tial\, a.
   Partaking of the same essence. -- Co`es*sen"tial*ly, adv.
   [1913 Webster]

         We bless and magnify that coessential Spirit, eternally
         proceeding from both [The Father and the Son].
                                                  --Hooker.
   [1913 Webster]