Source : Webster's Revised Unabridged Dictionary (1913)

Sophism \Soph"ism\, n. [F. sophisme, L. sophisma, fr. Gr. ?, fr.
   ? to make wise, ? to be become wise, to play the sophist, fr.
   ? wise.]
   The doctrine or mode of reasoning practiced by a sophist;
   hence, any fallacy designed to deceive.

         When a false argument puts on the appearance of a true
         one, then it is properly called a sophism, or
         ``fallacy''.                             --I. Watts.

         Let us first rid ourselves of sophisms, those of
         depraved men, and those of heartless philosophers. --I.
                                                  Taylor.

Source : WordNet®

sophism
     n : a deliberately invalid argument displaying ingenuity in
         reasoning in the hope of deceiving someone [syn: {sophistry},
          {sophistication}]