The Collaborative International Dictionary of English v.0.48:

Imitation \Im"i*ta"tion\, n. [L. imitatio: cf. F. imitation.]
   1. The act of imitating.
      [1913 Webster]

            Poesy is an art of imitation, . . . that is to say,
            a representing, counterfeiting, or figuring forth.
                                                  --Sir P.
                                                  Sidney.
      [1913 Webster]

   2. That which is made or produced as a copy; that which is
      made to resemble something else, whether for laudable or
      for fraudulent purposes; likeness; resemblance.
      [1913 Webster]

            Both these arts are not only true imitations of
            nature, but of the best nature.       --Dryden.
      [1913 Webster]

   3. (Mus.) One of the principal means of securing unity and
      consistency in polyphonic composition; the repetition of
      essentially the same melodic theme, phrase, or motive, on
      different degrees of pitch, by one or more of the other
      parts of voises. Cf. Canon.
      [1913 Webster]

   4. (Biol.) The act of condition of imitating another species
      of animal, or a plant, or unanimate object. See Imitate,
      v. t., 3.
      [1913 Webster]

   Note: Imitation is often used adjectively to characterize
         things which have a deceptive appearance, simulating
         the qualities of a superior article; -- opposed to
         real or genuine; as, imitation lace; imitation
         bronze; imitation modesty, etc.
         [1913 Webster]

WordNet (r) 3.0 (2006):

imitation
    adj 1: not genuine or real; being an imitation of the genuine
           article; "it isn't fake anything; it's real synthetic
           fur"; "faux pearls"; "false teeth"; "decorated with
           imitation palm leaves"; "a purse of simulated alligator
           hide" [syn: fake, false, faux, imitation,
           simulated]
    n 1: the doctrine that representations of nature or human
         behavior should be accurate imitations [ant: formalism]
    2: something copied or derived from an original
    3: copying (or trying to copy) the actions of someone else
    4: a representation of a person that is exaggerated for comic
       effect [syn: caricature, imitation, impersonation]

Moby Thesaurus II by Grady Ward, 1.0:

302 Moby Thesaurus words for "imitation":
   accordance, acting, adoption, affected, agent, agreement, alike,
   alikeness, alliance, alternate, alternative, analogy, aped, aping,
   apocryphal, approach, appropriation, approximation, artificial,
   assimilation, assumed, assumption, backup, bastard, bogus,
   borrowed plumes, brummagem, burlesque, caricature, certified copy,
   change, changeling, characterization, cheat, clinquant, closeness,
   colorable, colored, community, comparability, comparison,
   conduplication, conformity, consimilar, copied, copy, copying,
   correspondence, counterfeit, counterfeited, counterpart, deputy,
   derivation, deriving, distorted, double, doubling, dressed up,
   dumb show, dummy, duplicate, duplication, echo, ectype,
   embellished, embodiment, embroidered, emulation, enacting,
   enactment, equal, equivalent, ersatz, exchange, facsimile,
   factitious, fair copy, faithful copy, fake, faked, fakement, false,
   falsified, farce, favoring, feigned, fictitious, fictive, fill-in,
   following, forged, forgery, frame-up, fraud, garbled, gemination,
   ghost, ghostwriter, hoax, hokey, homogeneous, icon, identical,
   identity, illegitimate, image, imitated, impersonating,
   impersonation, impostor, impression, incarnation, infringement,
   ingemination, iteration, junk, junky, knockoff, lampoon, like,
   likeness, likening, locum tenens, make-believe, makeshift,
   man-made, masquerade, metaphor, metonymy, mimesis, mimicked,
   mimicking, mimicry, miming, mock, mock-up, mockery, mocking, model,
   nearly reproduced, nearness, next best thing, not unlike,
   palingenesis, pantomime, pantomiming, parallelism, paraphrase,
   parity, parody, paste, pasticcio, pastiche, performance,
   performing, personation, personification, personnel, perverted,
   phony, picture, pinch, pinch hitter, pinchbeck, pirating,
   plagiarism, plagiarized, plagiary, playing, portrait, portrayal,
   posing, pretended, provisional, proxy, pseudo, put-on, put-up job,
   quasi, queer, quotation, re-creation, re-formation, reappearance,
   rebirth, rebuilding, reconstitution, reconstruction, recurrence,
   redesign, redoing, redoubling, reduplication, reecho, reedition,
   reestablishment, refashioning, regeneration, regenesis,
   regurgitation, reincarnation, reinstitution, reissue, reiteration,
   relief, remaking, renascence, renewal, renovation, reoccurrence,
   reorganization, repetition, replacement, replica, replication,
   representation, representative, reprinting, reproduction,
   resemblance, resembling, reserve, reserves, reshaping, restoration,
   restructuring, resumption, resurrection, return, revision, revival,
   ringer, rip-off, sameness, satire, second string, secondary,
   self-styled, semblance, sham, shoddy, sign, similar, similarity,
   simile, similitude, simulacrum, simulated, simulation, smacking of,
   so-called, soi-disant, something like, spare, spares, spurious,
   squib, stand-in, stopgap, sub, substituent, substitute,
   substitution, succedaneum, suggestive of, superseder, supplanter,
   supposititious, surrogate, swindle, symbol, synecdoche, synthetic,
   take-off, takeoff, taking, temporary, tentative, third string, tin,
   tinsel, titivated, token, travesty, twinning, twisted, unauthentic,
   understudy, ungenuine, uniform with, unnatural, unreal, utility,
   utility player, version, vicar, vicarious, vice-president,
   vice-regent, warped, whited sepulcher, wicked imitation