The Collaborative International Dictionary of English v.0.48:

Non sequitur \Non seq"ui*tur\ [L., it does not follow.] (Logic)
   An inference which does not follow from the premises.
   [1913 Webster]

WordNet (r) 3.0 (2006):

non sequitur
    n 1: a reply that has no relevance to what preceded it
    2: (logic) a conclusion that does not follow from the premises

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "non sequitur":
   argument, argument by analogy, argumentum ad baculum,
   argumentum ad captandum, argumentum ad hominem, bad case,
   begging the question, broken thread, brokenness, circular argument,
   claptrap, crowd-pleasing argument, disconnectedness, disconnection,
   discontinuance, discontinuation, discontinuity, discontinuousness,
   discreteness, disjunction, empty words, episode, fallacy,
   fitfulness, formal fallacy, hysteron proteron, incoherence,
   incompleteness, insincere argument, intermittence, irregularity,
   logical fallacy, material fallacy, mere rhetoric, moonshine,
   noncontinuance, nonlinearity, nonseriality, nonuniformity,
   paralogism, parenthesis, petitio principii, philosophism,
   pseudosyllogism, solecism, sophism, sophistry, verbal fallacy,
   weak point