Source : Webster's Revised Unabridged Dictionary (1913)

Choir \Choir\, n. [OE. quer, OF. cuer, F. ch[oe]ur, fr. L.
   chorus a choral dance, chorus, choir, fr. Gr. ?, orig.
   dancing place; prob. akin to ? inclosure, L. hortus garden,
   and E. yard. See {Chorus}.]
   1. A band or organized company of singers, especially in
      church service. [Formerly written also {quire}.]

   2. That part of a church appropriated to the singers.

   3. (Arch.) The chancel.

   {Choir organ} (Mus.), one of the three or five distinct
      organs included in the full organ, each separable from the
      rest, but all controlled by one performer; a portion of
      the full organ, complete in itself, and more practicable
      for ordinary service and in the accompanying of the vocal
      choir.

   {Choir screen}, {Choir wall} (Arch.), a screen or low wall
      separating the choir from the aisles.

   {Choir service}, the service of singing performed by the
      choir. --T. Warton.

Source : WordNet®

choir
     n 1: a chorus that sings as part of a religious ceremony
     2: a family of similar musical instrument playing together
        [syn: {consort}]
     3: the area occupied by singers; the part of the chancel
        between sanctuary and nave

choir
     v : sing in a choir [syn: {chorus}]