The Collaborative International Dictionary of English v.0.48:

Excommunicate \Ex"com*mu"ni*cate\, a. [L. excommunicatus, p. p.
   of communicare to excommunicate; ex out + communicare. See
   Communicate.]
   Excommunicated; interdicted from the rites of the church. --
   n. One excommunicated.
   [1913 Webster]

         Thou shalt stand cursed and excommunicate. --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Excommunicate \Ex`com*mu"ni*cate\, v. t. [imp. & p. p.
   Excommunicated; p. pr. & vb. n. Excommunicating.]
   1. To put out of communion; especially, to cut off, or shut
      out, from communion with the church, by an ecclesiastical
      sentence.
      [1913 Webster]

   2. To lay under the ban of the church; to interdict.
      [1913 Webster]

            Martin the Fifth . . . was the first that
            excommunicated the reading of heretical books.
                                                  --Miltin.
      [1913 Webster]

WordNet (r) 3.0 (2006):

excommunicate
    v 1: exclude from a church or a religious community; "The gay
         priest was excommunicated when he married his partner"
         [syn: excommunicate, unchurch, curse] [ant:
         communicate]
    2: oust or exclude from a group or membership by decree