The Collaborative International Dictionary of English v.0.48:

Synod \Syn"od\ (s[i^]n"[u^]d), n. [L. synodus, Gr. sy`nodos a
   meeting; sy`n with + "odo`s a way; cf. AS. sino[eth],
   seno[eth], F. synode, both from the Latin.]
   1. (Eccl. Hist.) An ecclesiastic council or meeting to
      consult on church matters.
      [1913 Webster]

   Note: Synods are of four kinds: 1. General, or ecumenical,
         which are composed of bishops from different nations;
         -- commonly called general council. 2. National,
         composed of bishops of one nation only. 3. Provincial,
         in which the bishops of only one province meet; --
         called also convocations. 4. Diocesan, a synod in which
         the bishop of the diocese or his representative
         presides. Among Presbyterians, a synod is composed of
         several adjoining presbyteries. The members are the
         ministers and a ruling elder from each parish.
         [1913 Webster]

   2. An assembly or council having civil authority; a
      legislative body.
      [1913 Webster]

            It hath in solemn synods been decreed,
            Both by the Syracusians and ourselves,
            To admit no traffic to our adverse towns. --Shak.
      [1913 Webster]

            Parent of gods and men, propitious Jove!
            And you, bright synod of the powers above. --Dryden.
      [1913 Webster]

   3. (Astron.) A conjunction of two or more of the heavenly
      bodies. [R.] --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

synod
    n 1: a council convened to discuss ecclesiastical business

Moby Thesaurus II by Grady Ward, 1.0:

106 Moby Thesaurus words for "synod":
   British Cabinet, Council of Nicaea, Council of Trent,
   Lateran Council, Sanhedrin, US Cabinet, Vatican Council,
   advisory body, archbishopric, archdiocese, assemblee, assembly,
   assignation, association, at home, ball, bench, bishopric, board,
   body of advisers, borough council, brain trust, brawl, cabinet,
   camarilla, caucus, chamber, chapter, city council, classis,
   colloquium, commission, committee, common council, conciliarism,
   conclave, concourse, conference, congregation, congress,
   consistory, consultative assembly, conventicle, convention,
   convocation, council, council fire, council of ministers,
   council of state, council of war, county council, court, dance,
   date, deliberative assembly, diet, diocesan conference, diocese,
   directory, divan, ecclesiastical council, ecumenical council,
   eisteddfod, festivity, fete, forgathering, forum, gathering,
   get-together, housewarming, junta, kitchen cabinet, legislature,
   levee, meet, meeting, panel, parish, parish council,
   parochial church council, parochial council, party,
   plenary council, plenum, presbytery, privy council, prom, province,
   quorum, rally, reception, rendezvous, seance, see, session,
   shindig, sit-in, sitting, soiree, soviet, staff, symposium,
   syndicate, tribunal, turnout, vestry