Webster's Revised Unabridged Dictionary · 1913

Invitatory

Invitatory , adjective

[Latin invitatorius: compare French invitatoire.]

Using or containing invitations.
The “Venite” [Psalm xcv.], which is also called the invitatory psalm. — Hook

Invitatory , noun

[Late Latin invitatorium: compare French invitatoire.]

That which invites; specifically, the invitatory psalm, or a part of it used in worship.