manuductor

from The Century Dictionary.

• noun One who leads by the hand; a leader; a guide; specifically, in medieval music, one who indicated the rhythm to a choir by beating time with his hand or by striking pieces of wood or shell together; a conductor.

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

• noun (Mus.) A conductor; an officer in the ancient church who gave the signal for the choir to sing, and who beat time with the hand, and regulated the music.

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

• noun Catholicism The chief novice in an order.