The Collaborative International Dictionary of English v.0.48:

Chimerical \Chi*mer"ic*al\, a.
   Merely imaginary; fanciful; fantastic; wildly or vainly
   conceived; having, or capable of having, no existence except
   in thought; as, chimerical projects.

   Syn: Imaginary; fanciful; fantastic; wild; unfounded; vain;
        deceitful; delusive.
        [1913 Webster]

WordNet (r) 3.0 (2006):

chimerical
    adj 1: being or relating to or like a chimera; "his Utopia is
           not as chimeric commonwealth but a practical improvement
           on what already exists"- Douglas Bush [syn: chimeric,
           chimerical, chimeral]
    2: produced by a wildly fanciful imagination; "his Utopia is not
       a chimerical commonwealth but a practical improvement on what
       already exists"- Douglas Bush

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "chimerical":
   Barmecidal, Barmecide, absurd, aerial, air-built, airy, ambitious,
   apparent, apparitional, autistic, chimeric, cloud-born,
   cloud-built, cloud-woven, deceptive, delusional, delusionary,
   delusive, delusory, dereistic, dreamlike, dreamy, erroneous,
   ethereal, fabulous, fallacious, false, fanciful, fantastic,
   fatuitous, fatuous, fictional, fictive, gaseous, gossamery,
   illusional, illusionary, illusive, illusory, imaginary, misleading,
   mythical, ostensible, phantasmagoric, phantasmal, phantom,
   phantomlike, preposterous, pretentious, rarefied, seeming,
   self-deceptive, self-deluding, shadowy, specious, spectral,
   spirituous, subtile, subtle, supposititious, tenuous, unactual,
   unfounded, unreal, unsubstantial, utopian, vaporous, vapory,
   visionary, windy