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.
      [1913 Webster]

            This last petition heard of all her prayer.
                                                  --Dryden.
      [1913 Webster]

   2. A formal written request addressed to an official person,
      or to an organized body, having power to grant it.
      [1913 Webster]

   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).
      [1913 Webster]

   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.
      [1913 Webster]

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.
   [1913 Webster]

         You have . . . petitioned all the gods for my
         prosperity.                              --Shak.
   [1913 Webster]

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

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "petition":
   Angelus, Ave, Ave Maria, Hail Mary, Kyrie Eleison, Paternoster,
   address, aid prayer, appeal, appeal to, application, apply for,
   apply to, ask, asking, beadroll, beads, beg, beseech, beseechment,
   bidding prayer, breviary, call on, call upon, chaplet,
   circulate a petition, collect, commune with God, communion,
   contemplation, demand, desire, devotions, entreat, entreaty,
   expressed desire, give thanks, grace, impetration, imploration,
   implore, importune, imprecation, indent, intercession, invocation,
   invoke, litany, make supplication, meditation, memorialize,
   obsecration, obtestation, offer a prayer, orison, plea, plead,
   pray, pray over, prayer, prayer wheel, prefer a petition,
   recite the rosary, request, requisition, return thanks, rogation,
   rosary, say grace, sign a petition, silent prayer, solicit,
   solicitation, sue, suit, supplicate, supplication, thanks,
   thanksgiving, wish