What is a precentor? (From Golding's Lord of the Flies)

A person who directs a church choir or congregation in singing.

Then one of the boys flopped on his face in the sand and the line broke up. They heaved the falled boy to the platform and let him lie . . . .
"He's always throwing a faint," said Merridew. "He did in Gib,; and Addis; and at matin over the precentor."
This last piece of shop brought sniggers from the choir, who perched like black birds on the criss-cross trunks and examined Ralph with interest.
From Golding's Lord of the Flies.