'Tonsure' definitions:

Definition of 'tonsure'

noun

The shaved crown of a monk's or priest's head

noun

Shaving the crown of the head by priests or members of a monastic order

verb

Shave the head of a newly inducted monk

From: GCIDE

Tonsure \Ton"sure\, n. [F., fr. L. tonsura a shearing, clipping, from tondere, tonsum, to shear, shave; cf. Gr. ? to gnaw; perhaps akin to Gr. ? to cut, and E. tome.]
1. The act of clipping the hair, or of shaving the crown of the head; also, the state of being shorn. [1913 Webster]
2. (R. C. Ch.) (a) The first ceremony used for devoting a person to the service of God and the church; the first degree of the clericate, given by a bishop, abbot, or cardinal priest, consisting in cutting off the hair from a circular space at the back of the head, with prayers and benedictions; hence, entrance or admission into minor orders. (b) The shaven corona, or crown, which priests wear as a mark of their order and of their rank. [1913 Webster]