The Collaborative International Dictionary of English v.0.48:

paradox \par"a*dox\ (p[a^]r"[.a]*d[o^]ks), n.; pl. paradoxes
   (p[a^]r"[.a]*d[o^]ks*[e^]z). [F. paradoxe, L. paradoxum, fr.
   Gr. para`doxon; para` beside, beyond, contrary to + dokei^n
   to think, suppose, imagine. See Para-, and Dogma.]
   A tenet or proposition contrary to received opinion; an
   assertion or sentiment seemingly contradictory, or opposed to
   common sense; that which in appearance or terms is absurd,
   but yet may be true in fact.
   [1913 Webster]

         A gloss there is to color that paradox, and make it
         appear in show not to be altogether unreasonable.
                                                  --Hooker.
   [1913 Webster]

         This was sometime a paradox, but now the time gives it
         proof.                                   --Shak.
   [1913 Webster]

   Hydrostatic paradox. See under Hydrostatic.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "paradox":
   Gordian knot, absurdity, ambiguity, ambivalence, antinomy,
   asymmetry, contradiction, crux, dilemma, disproportion,
   disproportionateness, enigma, equivocality, equivocation, heresy,
   heterodoxy, heterogeneity, hopelessness, impossibility, impossible,
   impossibleness, incoherence, incommensurability, incompatibility,
   inconceivability, incongruity, inconsistency, inconsonance, irony,
   irreconcilability, knot, knotty point, mystery, no chance, node,
   nodus, nonconformability, nonconformity, nonplus, oxymoron,
   perplexity, pons asinorum, poser, problem, puzzle, quandary,
   self-contradiction, teaser, the impossible, unconformability,
   unconformity, unimaginability, unorthodoxy, unthinkability,
   vexed question, what cannot be, what cannot happen