The Collaborative International Dictionary of English v.0.48:

Illusory \Il*lu"so*ry\, a. [Cf. F. illusore.]
   Deceiving, or tending of deceive; fallacious; illusive; as,
   illusory promises or hopes.
   [1913 Webster]

WordNet (r) 3.0 (2006):

illusory
    adj 1: based on or having the nature of an illusion; "illusive
           hopes of finding a better job"; "Secret activities offer
           presidents the alluring but often illusory promise that
           they can achieve foreign policy goals without the
           bothersome debate and open decision that are staples of
           democracy" [syn: illusive, illusory]

Moby Thesaurus II by Grady Ward, 1.0:

131 Moby Thesaurus words for "illusory":
   Barmecidal, Barmecide, Circean, aberrant, abroad, adrift,
   air-built, airy, all abroad, all off, all wrong, amiss, apparent,
   apparitional, askew, astray, at fault, autistic, awry, beguiling,
   beside the mark, bewitching, catchy, charming, chimeric,
   chimerical, cloud-built, corrupt, deceiving, deceptive, defective,
   delusional, delusionary, delusive, delusory, dereistic, deviant,
   deviational, deviative, distorted, dreamlike, dreamy, dubious,
   enchanting, entrancing, errant, erring, erroneous, ethereal,
   fallacious, false, fancied, fanciful, fantastic, fascinating,
   fatuitous, fatuous, faultful, faulty, fictional, fictive, fishy,
   flawed, gaseous, glamorous, gossamery, hallucinatory, heretical,
   heterodox, illogical, illusional, illusionary, illusive, imaginary,
   imaginational, imagined, immaterial, merely nominal, misleading,
   mistaken, nonexistent, not real, not right, not true, notional,
   off, off the track, ostensible, out, peccant, perverse, perverted,
   phantasmagoric, phantasmal, phantom, phantomlike, questionable,
   rarefied, seeming, self-contradictory, self-deceptive,
   self-deluding, shadowy, specious, spectral, spellbinding,
   spirituous, straying, subtile, subtle, supposititious, tenuous,
   trickish, tricksy, tricky, unactual, unfactual, unfounded,
   unorthodox, unproved, unreal, unrealistic, unsubstantial, untrue,
   vaporous, visional, visionary, wide, windy, witching, wrong