The Collaborative International Dictionary of English v.0.48:

Solecism \Sol"e*cism\, n.[F. sol['e]cisme, L. soloecismus, Gr.
   soloikismo`s, fr. soloiki`zein to speak or write incorrectly,
   fr. so`loikos speaking incorrectly, from the corruption of
   the Attic dialect among the Athenian colonists of So`loi in
   Cilicia.]
   1. An impropriety or incongruity of language in the
      combination of words or parts of a sentence; esp.,
      deviation from the idiom of a language or from the rules
      of syntax.
      [1913 Webster]

            A barbarism may be in one word; a solecism must be
            of more.                              --Johnson.
      [1913 Webster]

   2. Any inconsistency, unfitness, absurdity, or impropriety,
      as in deeds or manners.
      [1913 Webster]

            Caesar, by dismissing his guards and retaining his
            power, committed a dangerous solecism in politics.
                                                  --C.
                                                  Middleton.
      [1913 Webster]

            The idea of having committed the slightest solecism
            in politeness was agony to him.       --Sir W.
                                                  Scott.
      [1913 Webster]

   Syn: Barbarism; impropriety; absurdity.
        [1913 Webster]

WordNet (r) 3.0 (2006):

solecism
    n 1: a socially awkward or tactless act [syn: faux pas,
         gaffe, solecism, slip, gaucherie]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "solecism":
   Irish bull, anachronism, anacoluthon, antiphrasis, argument,
   argument by analogy, argumentum ad baculum,
   argumentum ad captandum, argumentum ad hominem, bad case,
   barbarism, begging the question, bloomer, blooper, blunder, boner,
   boo-boo, boob, botch, breach, break, bull, bungle, catachresis,
   circular argument, claptrap, corruption, crowd-pleasing argument,
   empty words, error, fallacy, fault, faux pas, flub, fluff,
   folk etymology, formal fallacy, fumble, gaffe, gaucherie,
   grammatical error, hypercorrection, hyperform, hysteron proteron,
   impropriety, incongruity, inconsistency, indecorum, indiscretion,
   infelicity, insincere argument, lapse, logical fallacy, malaprop,
   malapropism, marrowsky, material fallacy, mere rhetoric,
   misconstruction, mispronunciation, missaying, mistake, misusage,
   moonshine, non sequitur, paralogism, petitio principii,
   philosophism, pseudosyllogism, slip, sophism, sophistry,
   spoonerism, stupidity, ungrammaticism, verbal fallacy,
   vernacularism, violation, vulgarism, weak point