invitatory

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

• noun A psalm or other piece sung as an invitation to prayer in church services, especially at the opening of matins in the Roman office.
• adjective Constituting or containing an invitation.

from The Century Dictionary.

• Using or containing invitation.
• noun A form of invitation used in religious worship; something consisting of or containing invitation in church service.
• noun Specifically— A form of exhortation to praise; especially, in the daily office of the Western Church, the variable antiphon to the Venite at matins. In the Anglican matins or morning prayer the versicle “Praise ye the Lord” (founded on the former “Alleluia” or “Laus tibi”), with its response, “The Lord's name be praised,” serves as unvarying invitatory. In the Greek Church the invariable invitatory is the triple “O come, let us worship … (Δευ%21τε, προσκυνήσ, σ1ωμεν …)” before the psalms at each of the canonical hours.
• noun An early name of the Roman introit.
• noun Any text of Scripture chosen for the day, and used before the Venite or 95th Psalm.

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

• adjective Using or containing invitations.
• noun That which invites; specifically, the invitatory psalm, or a part of it used in worship.

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

• adjective Of or pertaining to an invitation
• noun music A psalm sung, as an invitation to prayer, at the beginning of some services

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

• adjective conveying an invitation