Merriam-Webster's Collegiate® Dictionary, 11th Edition
CHOIR
I. noun see: chorus
Date: 14th century
an organized company of singers (as in a church service), a group of instruments of the same class , an organized group of persons or things, a division of angels, the part of a church occupied by the singers or by the clergy, a group organized for ensemble speaking,
II. intransitive verb
Date: 1596
to sing or sound in chorus or concert