Sacristy

Webster's Dictionary

(n.) An apartment in a church where the sacred utensils, vestments, etc., are kept; a vestry.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature

an apartment in a church or convent in which are kept the sacred objects used in the public worship, and in which the clergy and other public functionaries who take part in the service assemble and prepare for the ceremonies on which they are about to enter. In many churches the sacristy is a spacious and costly building.