Invocation

in·vo·ca·tion

1. the act of invoking or calling upon a deity, spirit, etc., for aid, protection, inspiration, or the like; supplication.
2. any petitioning or supplication for help or aid.
3. a form of prayer invoking God's presence, esp. one said at the beginning of a religious service or public ceremony.
4. an entreaty for aid and guidance from a Muse, deity, etc., at the beginning of an epic or epiclike poem.

Source
"invocation." Dictionary.com Unabridged (v 1.1). Random House, Inc. 13 Oct. 2008. .
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