cantor

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The Jewish religious official who leads the musical part of a service.
• noun The person who leads a church choir or congregation in singing; a precentor.

from The Century Dictionary.

• noun Eccles., an officer whose duty is to lead the singing in a cathedral or in a collegiate or parish church; a precentor.
• noun Specifically, in Germany, the music-master in a choir-school or similar institution, or the kapellmeister of a church. See kapellmeister.

from the GNU version of the Collaborative International Dictionary of English.

• noun A singer; esp. the leader of a church choir; a precentor.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun singer, especially someone who takes a special role of singing or song leading at a ceremony

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the official of a synagogue who conducts the liturgical part of the service and sings or chants the prayers intended to be performed as solos
• noun the musical director of a choir