Source : Webster's Revised Unabridged Dictionary (1913)

Foolishness \Fool"ish*ness\, n.
   1. The quality of being foolish.

   2. A foolish practice; an absurdity.

            The preaching of the cross is to them that perish
            foolishness.                          --1 Cor. i.
                                                  18.

Source : WordNet®

foolishness
     n 1: the trait of acting stupidly or rashly [syn: {folly}, {unwiseness}]
          [ant: {wisdom}]
     2: the quality of being rash and foolish [syn: {folly}, {craziness}]
     3: a stupid mistake [syn: {stupidity}, {betise}, {folly}, {imbecility}]