The Collaborative International Dictionary of English v.0.48:

choirmaster \choir"mas*ter\ n.
   the musical director of a choir.

   Syn: precentor, cantor.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

choirmaster
    n 1: the musical director of a choir [syn: choirmaster,
         precentor, cantor]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "choirmaster":
   Mahdi, bell cow, bell mare, bellwether, born leader, cantor,
   charismatic leader, choir chaplain, choragus, choral director,
   chorister, conductor, coryphaeus, duce, file leader, forerunner,
   fugleman, inspired leader, leader, leader of men, messiah,
   minister of music, pacemaker, pacesetter, precentor, ringleader,
   standard-bearer, symphonic conductor, torchbearer