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]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "lampoon":
   Atticism, agile wit, black humor, burlesque, caricature, comedy,
   dry wit, esprit, farce, hatchet job, hit off on, humor, imitation,
   irony, malicious parody, mock, mockery, nimble wit, parody,
   pasquil, pasquin, pasquinade, pastiche, pleasantry, poison pen,
   pretty wit, put down, quick wit, ready wit, ridicule, run down,
   salt, sarcasm, satire, satirize, savor of wit, send up, skewer,
   slapstick, slapstick humor, squib, subtle wit, take off,
   take off on, take-off, takeoff, travesty, visual humor,
   wicked imitation, wit