The Collaborative International Dictionary of English v.0.48:

Chorus \Cho"rus\, n.; pl. Choruses. [L., a dance in a ring, a
   dance accompanied with song; a chorus, a band of dancers and
   singers. Gr. ?. See Choir.]
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   1. (Antiq.) A band of singers and dancers.
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            The Grecian tragedy was at first nothing but a
            chorus of singers.                    --Dryden.
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   2. (Gr. Drama) A company of persons supposed to behold what
      passed in the acts of a tragedy, and to sing the
      sentiments which the events suggested in couplets or
      verses between the acts; also, that which was thus sung by
      the chorus.
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            What the lofty, grave tragedians taught
            In chorus or iambic.                  --Milton.
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   3. An interpreter in a dumb show or play. [Obs.]
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   4. (Mus.) A company of singers singing in concert.
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   5. (Mus.) A composition of two or more parts, each of which
      is intended to be sung by a number of voices.
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   6. (Mus.) Parts of a song or hymn recurring at intervals, as
      at the end of stanzas; also, a company of singers who join
      with the singer or choir in singer or choir in singing
      such parts.
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   7. The simultaneous of a company in any noisy demonstration;
      as, a Chorus of shouts and catcalls.
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