processional

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Of, relating to, or suitable for a procession.
• noun A book containing the rituals observed during a religious procession.
• noun A piece played or sung when the clergy enter a church at the beginning of a service.
• noun Music intended to be played or sung during a procession.

from The Century Dictionary.

• Pertaining to a procession; consisting in, having the movement of, or used in a procession: as, a processional hymn.
• noun An office-book containing the offices with their antiphons, hymns, rubrical directions, etc., for use in processional litanies and other religious processions.
• noun A hymn sung during a religious procession, particularly during the entry of the clergy and choir into the church before divine service.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Of or pertaining to a procession; consisting in a procession.
• noun (R. C. Ch.) A service book relating to ecclesiastical processions.
• noun A hymn, or other selection, sung during a church procession.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Of, pertaining to, or used during a procession
• noun A hymn or other music used during a procession; prosodion
• noun Roman Catholicism A service book relating to ecclesiastical processions.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective intended for use in a procession
• adjective of or relating to or characteristic of a procession
• noun religious music used in a procession