Source : Webster's Revised Unabridged Dictionary (1913)

Idiotism \Id"i*ot*ism\, n. [F. idiotisme, L. idiotismus the way
   of fashion of a private person, the common or vulgar manner
   of speaking, Gr. ?, fr. ? to put into or use common language,
   fr. ?. See {Idiot}.]
   1. An idiom; a form, mode of expression, or signification,
      peculiar to a language.

            Scholars sometimes give terminations and idiotisms,
            suitable to their native language, unto words newly
            invented.                             --M. Hale.

   2. Lack of knowledge or mental capacity; idiocy; foolishness.

            Worse than mere ignorance or idiotism.
                                                  --Shaftesbury.

            The running that adventure is the greatist idiotism.
                                                  --Hammond.