The Collaborative International Dictionary of English v.0.48:

Lampoon \Lam*poon"\, n. [F. lampon a drinking song, fr. lampons
   let us drink, -- the burden of such a song, fr. lamper to
   guzzle, to drink much and greedily; of German origin, and
   akin to E. lap to drink. Prob. so called because drinking
   songs often contain personal slander or satire.]
   1. A personal satire in writing; usually, malicious and
      abusive censure written only to reproach and distress.
      [1913 Webster]

            Like her who missed her name in a lampoon,
            And grieved to find herself decayed so soon.
                                                  --Dryden.
      [1913 Webster]

   2. Hence: Any satire ridiculing or mocking a person,
      activity, or institution by representing its character or
      behavior in an exaggerated or grotesque form; the
      representation may be written, filmed, or performed as a
      live skit, and may be intended as a severe reproach, or as
      good-natured humor.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Lampoon \Lam*poon"\, v. t. [imp. & p. p. Lampooned; p. pr. &
   vb. n. Lampooning.]
   To subject to abusive ridicule expressed in a work of art; to
   make (a person, behavior, or institution) the subject of a
   lampoon.
   [1913 Webster +PJC]

         Ribald poets had lampooned him.          --Macaulay.

   Syn: To libel; defame; satirize; lash.
        [1913 Webster]

WordNet (r) 3.0 (2006):

lampoon
    n 1: a composition that imitates or misrepresents somebody's
         style, usually in a humorous way [syn: parody, lampoon,
         spoof, sendup, mockery, takeoff, burlesque,
         travesty, charade, pasquinade, put-on]
    v 1: ridicule with satire; "The writer satirized the
         politician's proposal" [syn: satirize, satirise,
         lampoon]