It is an inflection of tonsorial. It means order as a priest. It is also shave part of the hair of the head (on the Crown), when it ordered a Catholic priest. Crown.
TONSURA:CEREMONIA THAT IS USED IN THE CLERICAL GRADES OF THE CATHOLIC CHURCH, CASE PART OF THE HAIR, TO RECEIVE THE SACRAMENT OF ORDERS.
Tonsure: f. preparatory level to receive the minor orders, which confers the prelate with the ceremony of cutting the applicant a little hair.