From The Collaborative International Dictionary of English v.0.48 [gcide]:
Prayer \Prayer\ (?; 277), n. [OE. preiere, OF. preiere, F.
pri[`e]re, fr. L. precarius obtained by prayer, fr. precari
to pray. See Pray, v. i.]
1. The act of praying, or of asking a favor; earnest request
or entreaty; hence, a petition or memorial addressed to a
court or a legislative body. "Their meek preyere."
--Chaucer
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2. The act of addressing supplication to a divinity,
especially to the true God; the offering of adoration,
confession, supplication, and thanksgiving to the Supreme
Being; as, public prayer; secret prayer.
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As he is famed for mildness, peace, and prayer.
--Shak.
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3. The form of words used in praying; a formula of
supplication; an expressed petition; especially, a
supplication addressed to God; as, a written or
extemporaneous prayer; to repeat one's prayers.
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He made those excellent prayers which were published
immediately after his death. --Bp. Fell.
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Prayer book, a book containing devotional prayers.
Prayer meeting, a meeting or gathering for prayer to God.
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Syn: Petition; orison; supplication; entreaty; suit.
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From WordNet (r) 3.0 (2006) [wn]:
prayer book
n 1: a book containing prayers [syn: prayer book,
prayerbook]