The Collaborative International Dictionary of English v.0.48:

Prayer \Pray"er\, n.
   One who prays; a supplicant.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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
      [1913 Webster]

   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.
      [1913 Webster]

            As he is famed for mildness, peace, and prayer.
                                                  --Shak.
      [1913 Webster]

   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.
      [1913 Webster]

            He made those excellent prayers which were published
            immediately after his death.          --Bp. Fell.
      [1913 Webster]

   Prayer book, a book containing devotional prayers.

   Prayer meeting, a meeting or gathering for prayer to God.
      [1913 Webster]

   Syn: Petition; orison; supplication; entreaty; suit.
        [1913 Webster]

WordNet (r) 3.0 (2006):

prayer
    n 1: the act of communicating with a deity (especially as a
         petition or in adoration or contrition or thanksgiving);
         "the priest sank to his knees in prayer" [syn: prayer,
         supplication]
    2: reverent petition to a deity [syn: prayer, petition,
       orison]
    3: earnest or urgent request; "an entreaty to stop the
       fighting"; "an appeal for help"; "an appeal to the public to
       keep calm" [syn: entreaty, prayer, appeal]
    4: a fixed text used in praying
    5: someone who prays to God [syn: prayer, supplicant]

Moby Thesaurus II by Grady Ward, 1.0:

102 Moby Thesaurus words for "prayer":
   Angelus, Ave, Ave Maria, Hail Mary, Kyrie Eleison, Mass,
   Paternoster, adjuration, adoration, aid prayer, appeal,
   application, asker, beadroll, beads, bedtime prayer, beggar,
   begging, beseeching, beseechment, bid, bidding prayer, breviary,
   call, camp meeting, chaplet, church, church service, clamor,
   collect, communion, compline, contemplation, cry, devotion,
   devotions, divine service, duty, entreaty, evening devotions,
   evensong, exercises, grace, impetration, imploration, imploring,
   imprecation, intercession, invocation, invocatory plea, lauds,
   litany, liturgy, matins, meditation, meeting, morning devotions,
   night song, none, nones, novena, obsecration, obtestation, office,
   orison, petition, petitioner, plea, pleading, praise meeting,
   prayer meeting, prayer wheel, prayers, praying, prime, prime song,
   public worship, request, revival, revival meeting, rogation,
   rosary, service, sext, silent prayer, suit, suitor, supplicant,
   supplication, supplicator, tent meeting, thanks, thanksgiving,
   tierce, undersong, vesper, vespers, vigils, watch meeting,
   watch night, watch-night service, worship



Easton's 1897 Bible Dictionary:

Prayer
   is converse with God; the intercourse of the soul with God, not
   in contemplation or meditation, but in direct address to him.
   Prayer may be oral or mental, occasional or constant,
   ejaculatory or formal. It is a "beseeching the Lord" (Ex.
   32:11); "pouring out the soul before the Lord" (1 Sam. 1:15);
   "praying and crying to heaven" (2 Chr. 32:20); "seeking unto God
   and making supplication" (Job 8:5); "drawing near to God" (Ps.
   73:28); "bowing the knees" (Eph. 3:14).

     Prayer presupposes a belief in the personality of God, his
   ability and willingness to hold intercourse with us, his
   personal control of all things and of all his creatures and all
   their actions.

     Acceptable prayer must be sincere (Heb. 10:22), offered with
   reverence and godly fear, with a humble sense of our own
   insignificance as creatures and of our own unworthiness as
   sinners, with earnest importunity, and with unhesitating
   submission to the divine will. Prayer must also be offered in
   the faith that God is, and is the hearer and answerer of prayer,
   and that he will fulfil his word, "Ask, and ye shall receive"
   (Matt. 7:7, 8; 21:22; Mark 11:24; John 14:13, 14), and in the
   name of Christ (16:23, 24; 15:16; Eph. 2:18; 5:20; Col. 3:17; 1
   Pet. 2:5).

     Prayer is of different kinds, secret (Matt. 6:6); social, as
   family prayers, and in social worship; and public, in the
   service of the sanctuary.

     Intercessory prayer is enjoined (Num. 6:23; Job 42:8; Isa.
   62:6; Ps. 122:6; 1 Tim. 2:1; James 5:14), and there are many
   instances on record of answers having been given to such
   prayers, e.g., of Abraham (Gen. 17:18, 20; 18:23-32; 20:7, 17,
   18), of Moses for Pharaoh (Ex. 8:12, 13, 30, 31; Ex. 9:33), for
   the Israelites (Ex. 17:11, 13; 32:11-14, 31-34; Num. 21:7, 8;
   Deut. 9:18, 19, 25), for Miriam (Num. 12:13), for Aaron (Deut.
   9:20), of Samuel (1 Sam. 7:5-12), of Solomon (1 Kings 8; 2 Chr.
   6), Elijah (1 Kings 17:20-23), Elisha (2 Kings 4:33-36), Isaiah
   (2 Kings 19), Jeremiah (42:2-10), Peter (Acts 9:40), the church
   (12:5-12), Paul (28:8).

     No rules are anywhere in Scripture laid down for the manner of
   prayer or the attitude to be assumed by the suppliant. There is
   mention made of kneeling in prayer (1 Kings 8:54; 2 Chr. 6:13;
   Ps. 95:6; Isa. 45:23; Luke 22:41; Acts 7:60; 9:40; Eph. 3:14,
   etc.); of bowing and falling prostrate (Gen. 24:26, 52; Ex.
   4:31; 12:27; Matt. 26:39; Mark 14:35, etc.); of spreading out
   the hands (1 Kings 8:22, 38, 54; Ps. 28:2; 63:4; 88:9; 1 Tim.
   2:8, etc.); and of standing (1 Sam. 1:26; 1 Kings 8:14, 55; 2
   Chr. 20:9; Mark 11:25; Luke 18:11, 13).

     If we except the "Lord's Prayer" (Matt. 6:9-13), which is,
   however, rather a model or pattern of prayer than a set prayer
   to be offered up, we have no special form of prayer for general
   use given us in Scripture.

     Prayer is frequently enjoined in Scripture (Ex. 22:23, 27; 1
   Kings 3:5; 2 Chr. 7:14; Ps. 37:4; Isa. 55:6; Joel 2:32; Ezek.
   36:37, etc.), and we have very many testimonies that it has been
   answered (Ps. 3:4; 4:1; 6:8; 18:6; 28:6; 30:2; 34:4; 118:5;
   James 5:16-18, etc.).

     "Abraham's servant prayed to God, and God directed him to the
   person who should be wife to his master's son and heir (Gen.
   24:10-20).

     "Jacob prayed to God, and God inclined the heart of his
   irritated brother, so that they met in peace and friendship
   (Gen. 32:24-30; 33:1-4).

     "Samson prayed to God, and God showed him a well where he
   quenched his burning thirst, and so lived to judge Israel (Judg.
   15:18-20).

     "David prayed, and God defeated the counsel of Ahithophel (2
   Sam. 15:31; 16:20-23; 17:14-23).

     "Daniel prayed, and God enabled him both to tell
   Nebuchadnezzar his dream and to give the interpretation of it
   (Dan. 2: 16-23).

     "Nehemiah prayed, and God inclined the heart of the king of
   Persia to grant him leave of absence to visit and rebuild
   Jerusalem (Neh. 1:11; 2:1-6).

     "Esther and Mordecai prayed, and God defeated the purpose of
   Haman, and saved the Jews from destruction (Esther 4:15-17; 6:7,
   8).

     "The believers in Jerusalem prayed, and God opened the prison
   doors and set Peter at liberty, when Herod had resolved upon his
   death (Acts 12:1-12).

     "Paul prayed that the thorn in the flesh might be removed, and
   his prayer brought a large increase of spiritual strength, while
   the thorn perhaps remained (2 Cor. 12:7-10).

     "Prayer is like the dove that Noah sent forth, which blessed
   him not only when it returned with an olive-leaf in its mouth,
   but when it never returned at all.", Robinson's Job.


Bouvier's Law Dictionary, Revised 6th Ed (1856):

PRAYER, chanc. pleadings. That part of a bill which asks for relief.
     2. The skill of the solicitor is to be exercised in framing this part
of the bill. An accurate specification of the matters to be decreed in
complicated cases, requires great discernment and experience; Coop. Eq. Pl.
13; it is varied as the case is made out, concluding always with a prayer of
general relief, at the discretion of the court. Mitf. Pl. 45.