The Collaborative International Dictionary of English v.0.48:

Precentor \Pre*cen"tor\, n. [L. praecentor, fr. praecinere to
   sing before; prae before + canere to sing. See Chant.]
   A leader of a choir; a directing singer. Specifically:
   (a) The leader of the choir in a cathedral; -- called also
       the chanter or master of the choir. --Hook.
   (b) The leader of the congregational singing in Scottish and
       other churches.
       [1913 Webster]

WordNet (r) 3.0 (2006):

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