The Collaborative International Dictionary of English v.0.48:

Sacristy \Sac"ris*ty\, n.; pl. Sacristies. [F. sacristie, LL.
   sacristia, fr. L. sacer. See Sacred.]
   An apartment in a church where the sacred utensils,
   vestments, etc., are kept; a vestry.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sacristy
    n 1: a room in a church where sacred vessels and vestments are
         kept or meetings are held [syn: vestry, sacristy]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "sacristy":
   Easter sepulcher, ambry, apse, baptistery, blindstory, chancel,
   choir, cloisters, confessional, confessionary, crypt, diaconicon,
   diaconicum, nave, porch, presbytery, rood loft, rood stair,
   rood tower, sacrarium, transept, triforium, vestry