The Collaborative International Dictionary of English v.0.48:

Communion \Com*mun"ion\, n. [L. communio: cf. F. communion. See
   Common.]
   1. The act of sharing; community; participation. "This
      communion of goods." --Blackstone.
      [1913 Webster]

   2. Intercourse between two or more persons; esp., intimate
      association and intercourse implying sympathy and
      confidence; interchange of thoughts, purposes, etc.;
      agreement; fellowship; as, the communion of saints.
      [1913 Webster]

            We are naturally induced to seek communion and
            fellowship with others.               --Hooker.
      [1913 Webster]

            What communion hath light with darkness? --2 Cor.
                                                  vi. 14.
      [1913 Webster]

            Bare communion with a good church can never alone
            make a good man.                      --South.
      [1913 Webster]

   3. A body of Christians having one common faith and
      discipline; as, the Presbyterian communion.
      [1913 Webster]

   4. The sacrament of the eucharist; the celebration of the
      Lord's supper; the act of partaking of the sacrament; as,
      to go to communion; to partake of the communion; called
      also Holy Communion.
      [1913 Webster +PJC]

   Close communion. See under Close, a.

   Communion elements, the bread and wine used in the
      celebration of the Lord's supper.

   Communion service, the celebration of the Lord's supper, or
      the office or service therefor.

   Communion table, the table upon which the elements are
      placed at the celebration of the Lord's supper.

   Communion in both kinds, participation in both the bread
      and wine by all communicants.

   Communion in one kind, participation in but one element, as
      in the Roman Catholic Church, where the laity partake of
      the bread only.

   Syn: Share; participation; fellowship; converse; intercourse;
        unity; concord; agreement.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Holy \Ho"ly\, a. [Compar. Holier; superl. Holiest.] [OE.
   holi, hali, AS. h[=a]lig, fr. h[ae]l health, salvation,
   happiness, fr. h[=a]l whole, well; akin to OS. h?lag, D. & G.
   heilig, OHG. heilac, Dan. hellig, Sw. helig, Icel. heilagr.
   See Whole, and cf. Halibut, Halidom, Hallow,
   Hollyhock.]
   1. Set apart to the service or worship of God; hallowed;
      sacred; reserved from profane or common use; holy vessels;
      a holy priesthood. "Holy rites and solemn feasts."
      --Milton.
      [1913 Webster]

   2. Spiritually whole or sound; of unimpaired innocence and
      virtue; free from sinful affections; pure in heart; godly;
      pious; irreproachable; guiltless; acceptable to God.
      [1913 Webster]

            Now through her round of holy thought
            The Church our annual steps has brought. --Keble.
      [1913 Webster]

   Holy Alliance (Hist.), a league ostensibly for conserving
      religion, justice, and peace in Europe, but really for
      repressing popular tendencies toward constitutional
      government, entered into by Alexander I. of Russia,
      Francis I. of Austria, and Frederic William III. of
      Prussia, at Paris, on the 26th of September, 1815, and
      subsequently joined by all the sovereigns of Europe,
      except the pope and the king of England.

   Holy bark. See Cascara sagrada.

   Holy Communion. See Eucharist.

   Holy family (Art), a picture in which the infant Christ,
      his parents, and others of his family are represented.

   Holy Father, a title of the pope.

   Holy Ghost (Theol.), the third person of the Trinity; the
      Comforter; the Paraclete.

   Holy Grail. See Grail.

   Holy grass (Bot.), a sweet-scented grass (Hierochloa
      borealis and Hierochloa alpina). In the north of Europe
      it was formerly strewed before church doors on saints'
      days; whence the name. It is common in the northern and
      western parts of the United States. Called also vanilla
      grass or Seneca grass.

   Holy Innocents' day, Childermas day.

   Holy Land, Palestine, the birthplace of Christianity.

   Holy office, the Inquisition.

   Holy of holies (Script.), the innermost apartment of the
      Jewish tabernacle or temple, where the ark was kept, and
      where no person entered, except the high priest once a
      year.

   Holy One.
      (a) The Supreme Being; -- so called by way of emphasis. "
          The Holy One of Israel." --Is. xliii. 14.
      (b) One separated to the service of God.

   Holy orders. See Order.

   Holy rood, the cross or crucifix, particularly one placed,
      in churches. over the entrance to the chancel.

   Holy rope, a plant, the hemp agrimony.

   Holy Saturday (Eccl.), the Saturday immediately preceding
      the festival of Easter; the vigil of Easter.

   Holy Spirit, same as Holy Ghost (above).

   Holy Spirit plant. See Dove plant.

   Holy thistle (Bot.), the blessed thistle. See under
      Thistle.

   Holy Thursday. (Eccl.)
      (a) (Episcopal Ch.) Ascension day.
      (b) (R. C. Ch.) The Thursday in Holy Week; Maundy
          Thursday.

   Holy war, a crusade; an expedition carried on by Christians
      against the Saracens in the Holy Land, in the eleventh,
      twelfth, and thirteenth centuries, for the possession of
      the holy places.

   Holy water (Gr. & R. C. Churches), water which has been
      blessed by the priest for sacred purposes.

   Holy-water stoup, the stone stoup or font placed near the
      entrance of a church, as a receptacle for holy water.

   Holy Week (Eccl.), the week before Easter, in which the
      passion of our Savior is commemorated.

   Holy writ, the sacred Scriptures. " Word of holy writ."
      --Wordsworth.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Holy Communion
    n 1: the act of participating in the celebration of the
         Eucharist; "the governor took Communion with the rest of
         the congregation" [syn: Communion, Holy Communion,
         sacramental manduction, manduction]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "Holy Communion":
   Communion, Eucharist, Host, Last Supper, Sacrament Sunday,
   altar bread, bread, bread and wine, consecrated bread,
   consecrated elements, consubstantiation, elements, impanation,
   intinction, loaf, real presence, subpanation, the Holy Sacrament,
   the Sacrament, transubstantiation, wafer