The Collaborative International Dictionary of English v.0.48:

Paralogism \Pa*ral"o*gism\, n. [Gr. paralogismo`s, fr.
   paralogi`zesqai to reason falsely; para` beside + logi`zesqai
   to reason, lo`gos discourse, reason: cf. F. paralogisme.]
   (Logic)
   A reasoning which is false in point of form, that is, which
   is contrary to logical rules or formul[ae]; a formal fallacy,
   or pseudo-syllogism, in which the conclusion does not follow
   from the premises.
   [1913 Webster]

WordNet (r) 3.0 (2006):

paralogism
    n 1: an unintentionally invalid argument

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "paralogism":
   Aristotelian sorites, Goclenian sorites, argument,
   argument by analogy, argumentum ad baculum,
   argumentum ad captandum, argumentum ad hominem, bad case,
   begging the question, categorical syllogism, circular argument,
   claptrap, crowd-pleasing argument, dilemma, empty words, enthymeme,
   fallacy, figure, formal fallacy, hysteron proteron,
   insincere argument, logical fallacy, material fallacy,
   mere rhetoric, mode, modus tollens, mood, moonshine, non sequitur,
   petitio principii, philosophism, prosyllogism, pseudosyllogism,
   rule, rule of deduction, solecism, sophism, sophistry, sorites,
   syllogism, verbal fallacy, weak point