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

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "excommunicate":
   accurse, anathematize, attaint, ban, banish, blackball, blacklist,
   blaspheme, blast, break, bring home to, bust, cashier, cast out,
   censure, condemn, confound, convict, curse, cut, damn, darn,
   deconsecrate, defrock, denounce, denunciate, deport, depose,
   dethrone, disbar, discrown, disenthrone, disfellowship, dismiss,
   displace, doom, drum out, exclude, execrate, exile, expatriate,
   expel, extradite, find guilty, fugitate, fulminate against,
   give the gate, hex, imprecate, kick upstairs, liquidate, ostracize,
   oust, outlaw, overthrow, pass sentence on, penalize, pension,
   pension off, pronounce judgment, pronounce sentence, proscribe,
   purge, read out of, relegate, remove, remove from office, retire,
   rusticate, send to Coventry, sentence, snub, spurn,
   strip of office, strip of rank, superannuate, suspend,
   throw a whammy, thrust out, thunder against, transport, unchurch,
   unfrock, unsaddle, unseat, unthrone