The Collaborative International Dictionary of English v.0.48:

Congregation \Con`gre*ga"tion\, n. [L. congregatio: cf. F.
   congr['e]gation.]
   1. The act of congregating, or bringing together, or of
      collecting into one aggregate or mass.
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            The means of reduction in the fire is but by the
            congregation of homogeneal parts.     --Bacon.
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   2. A collection or mass of separate things.
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            A foul and pestilent congregation of vapors. --Shak.
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   3. An assembly of persons; a gathering; esp. an assembly of
      persons met for the worship of God, and for religious
      instruction; a body of people who habitually so meet.
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            He [Bunyan] rode every year to London, and preached
            there to large and attentive congregations.
                                                  --Macaulay.
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   4. (Anc. Jewish Hist.) The whole body of the Jewish people;
      -- called also Congregation of the Lord.
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            It is a sin offering for the congregation. --Lev.
                                                  iv. 21.
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   5. (R. C. Ch.)
      (a) A body of cardinals or other ecclesiastics to whom as
          intrusted some department of the church business; as,
          the Congregation of the Propaganda, which has charge
          of the missions of the Roman Catholic Church.
      (b) A company of religious persons forming a subdivision
          of a monastic order.
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   6. The assemblage of Masters and Doctors at Oxford or
      Cambrige University, mainly for the granting of degrees.
      [Eng.]
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   7. (Scotch Church Hist.) the name assumed by the Protestant
      party under John Knox. The leaders called themselves
      (1557) Lords of the Congregation.
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WordNet (r) 3.0 (2006):

congregation
    n 1: a group of people who adhere to a common faith and
         habitually attend a given church [syn: congregation,
         fold, faithful]
    2: an assemblage of people or animals or things collected
       together; "a congregation of children pleaded for his
       autograph"; "a great congregation of birds flew over"
    3: the act of congregating [syn: congregation, congregating]

Easton's 1897 Bible Dictionary:

Congregation
   (Heb. kahal), the Hebrew people collectively as a holy community
   (Num. 15:15). Every circumcised Hebrew from twenty years old and
   upward was a member of the congregation. Strangers resident in
   the land, if circumcised, were, with certain exceptions (Ex.
   12:19; Num. 9:14; Deut. 23:1-3), admitted to the privileges of
   citizenship, and spoken of as members of the congregation (Ex.
   12:19; Num. 9:14; 15:15). The congregation were summonded
   together by the sound of two silver trumpets, and they met at
   the door of the tabernacle (Num. 10:3). These assemblies were
   convened for the purpose of engaging in solemn religious
   services (Ex. 12:27; Num. 25:6; Joel 2:15), or of receiving new
   commandments (Ex. 19:7, 8). The elders, who were summonded by
   the sound of one trumpet (Num. 10:4), represented on various
   occasions the whole congregation (Ex. 3:16; 12:21; 17:5; 24:1).

     After the conquest of Canaan, the people were assembled only
   on occasions of the highest national importance (Judg. 20; 2
   Chr. 30:5; 34:29; 1 Sam. 10:17; 2 Sam. 5:1-5; 1 Kings 12:20; 2
   Kings 11:19; 21:24; 23:30). In subsequent times the congregation
   was represented by the Sanhedrim; and the name synagogue,
   applied in the Septuagint version exclusively to the
   congregation, came to be used to denote the places of worship
   established by the Jews. (See CHURCH.)

     In Acts 13:43, where alone it occurs in the New Testament, it
   is the same word as that rendered "synagogue" (q.v.) in ver. 42,
   and is so rendered in ver. 43 in R.V.