in·vi·ta·to·ry (ĭn-vī'tə-tôr'ē, -tōr'ē) n.
pl.in·vi·ta·to·ries A psalm or other piece sung as an invitation to prayer in church services, especially at the opening of matins in the Roman office. adj. Constituting or containing an invitation.
[Middle English invitatorie, from Medieval Latin invītātōrium, from Late Latin invītātōrius, inviting, from Latin invītātus, past participle of invītāre, to invite.]