The Collaborative International Dictionary of English v.0.48:

malapropism \mal"a*prop*ism\, n. [From Mrs. Malaprop, a
   character in Sheridan's drama, " The Rivals," who makes
   amusing blunders in her use of words. See Malapropos.]
   A grotesque misuse of a word; a word so used.
   [1913 Webster]

WordNet (r) 3.0 (2006):

malapropism
    n 1: the unintentional misuse of a word by confusion with one
         that sounds similar [syn: malapropism, malaprop]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "malapropism":
   Irish bull, abuse of terms, acrostic, alliteration, allusion,
   amphibologism, amphiboly, anacoluthon, anadiplosis, anagram,
   analogy, anaphora, anastrophe, antiphrasis, antithesis,
   antonomasia, apophasis, aporia, aposiopesis, apostrophe, barbarism,
   bull, calembour, catachresis, chiasmus, circumlocution, climax,
   conversion, corruption, ecphonesis, emphasis, equivocality,
   equivoque, exclamation, fluff, folk etymology, gemination,
   grammatical error, hypallage, hyperbaton, hyperbole,
   hypercorrection, hyperform, infelicity, inversion, irony,
   jeu de mots, litotes, logogram, logogriph, malaprop, marrowsky,
   meiosis, metagram, metaphor, metonymy, misconstruction,
   mispronunciation, missaying, misusage, onomatopoeia, oxymoron,
   palindrome, paregmenon, parenthesis, paronomasia, periphrasis,
   personification, play on words, pleonasm, preterition, prolepsis,
   pun, punning, regression, repetition, sarcasm, simile, similitude,
   solecism, spoonerism, syllepsis, symploce, synecdoche,
   ungrammaticism, wordplay, zeugma