The Collaborative International Dictionary of English v.0.48:

Petition \Pe*ti"tion\, n. [F. p['e]tition, L. petitio, fr.
   petere, petitum, to beg, ask, seek; perh. akin to E. feather,
   or find.]
   1. A prayer; a supplication; an imploration; an entreaty;
      especially, a request of a solemn or formal kind; a prayer
      to the Supreme Being, or to a person of superior power,
      rank, or authority; also, a single clause in such a
      prayer.
      [1913 Webster]

            A house of prayer and petition for thy people. --1
                                                  Macc. vii. 37.
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            This last petition heard of all her prayer.
                                                  --Dryden.
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   2. A formal written request addressed to an official person,
      or to an organized body, having power to grant it.
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   3. Specifically: (Law), A request to government, in either of
      its branches, for the granting of a particular grace or
      right, or for the legislature to take a specific action;
      -- in distinction from a memorial, which calls certain
      facts to mind. The petition may be signed by one or any
      number of persons.
      [1913 Webster + PJC]

   4. The written document containing a petition (senses 1 or
      2).
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   Petition of right (Law), a petition to obtain possession or
      restitution of property, either real or personal, from the
      Crown, which suggests such a title as controverts the
      title of the Crown, grounded on facts disclosed in the
      petition itself. --Mozley & W.

   The Petition of Right (Eng. Hist.), the parliamentary
      declaration of the rights of the people, assented to by
      Charles I.
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The Collaborative International Dictionary of English v.0.48:

Petition \Pe*ti"tion\, v. t. [imp. & p. p. Petitioned; p. pr.
   & vb. n. Petitioning.]
   To make a prayer or request to; to ask from; to solicit; to
   entreat; especially, to make a formal written supplication,
   or application to, as to any branch of the government; as, to
   petition the court; to petition the governor.
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         You have . . . petitioned all the gods for my
         prosperity.                              --Shak.
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The Collaborative International Dictionary of English v.0.48:

Petition \Pe*ti"tion\, v. i.
   To make a petition or solicitation.
   [1913 Webster]

WordNet (r) 3.0 (2006):

petition
    n 1: a formal message requesting something that is submitted to
         an authority [syn: request, petition, postulation]
    2: reverent petition to a deity [syn: prayer, petition,
       orison]
    v 1: write a petition for something to somebody; request
         formally and in writing