Source : Webster's Revised Unabridged Dictionary (1913)

Stupidity \Stu*pid"i*ty\, n. [L. stupiditas: cf. F.
   stupidit['e].]
   1. The quality or state of being stupid; extreme dullness of
      perception or understanding; insensibility; sluggishness.

   2. Stupor; astonishment; stupefaction. [R.]

            A stupidity Past admiration strikes me, joined with
            fear.                                 --Chapman.

Source : WordNet®

stupidity
     n 1: a poor ability to understand or to profit from experience
          [ant: {intelligence}]
     2: a stupid mistake [syn: {betise}, {folly}, {foolishness}, {imbecility}]