Real Dictionary

choir
countable noun: A choir is a group of people who sing together, for example in a church or school.

choir in American English
a group of singers organized and trained to sing together, esp. in a church
to sing or sound in chorus
adjective: professed to recite or chant the divine office
noun: a company of singers, esp. an organized group employed in church service

choir in British English
noun: an organized group of singers, esp for singing in church services or public performances