invocation

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

• noun The act or an instance of invoking, especially an appeal to a higher power for assistance.
• noun A prayer or other formula used in invoking, as at the opening of a religious service.
• noun The act of conjuring up a spirit by incantation.
• noun An incantation used in conjuring.

from The Century Dictionary.

• noun The act of invoking or calling in prayer; the form or act of summoning or inviting presence or aid: as, invocation of the Muses.
• noun In law, a judicial call, demand, or order: as, the invocation of papers or evidence into a court.
• noun Eccles.: An invoking of the blessing of God upon any undertaking; especially, an opening prayer in a public service invoking divine blessing upon it; specifically, the words “In nomine Patris, et Filii, et Spiritus Sancti. Amen,” “In the name of the Father, and of the Son, and of the Holy Ghost. Amen,” used at the beginning of the Roman mass, before sermons in many Anglican churches, and on other occasions.
• noun The third part of the prayer of consecration in the communion office of the American Book of Common Prayer, in the Scottish office of 1764 (from which that prayer is derived), and in the Nonjurors' office of 1718, on which, as well as on earlier Scottish and English offices and ancient Oriental liturgies, the Scottish office of 1764 is based.
• noun In the Roman Catholic and Anglican litanies, one of the petitions addressed to God in each person and in Trinity, and to the saints.

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

• noun The act or form of calling for the assistance or presence of some superior being; earnest and solemn entreaty; esp., prayer offered to a divine being.
• noun (Law) A call or summons; especially, a judicial call, demand, or order.

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

• noun The act or form of calling for the assistance or presence of some superior being; earnest and solemn entreaty; esp., prayer offered to a divine being.
• noun A call or summons; especially, a judicial call, demand, or order; as, the invocation of papers or evidence into court.

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

• noun calling up a spirit or devil
• noun the act of appealing for help
• noun a prayer asking God's help as part of a religious service
• noun an incantation used in conjuring or summoning a devil