Source : Webster's Revised Unabridged Dictionary (1913)

Foolish \Fool"ish\, a.
   1. Marked with, or exhibiting, folly; void of understanding;
      weak in intellect; without judgment or discretion; silly;
      unwise.

            I am a very foolish fond old man.     --Shak.

   2. Such as a fool would do; proceeding from weakness of mind
      or silliness; exhibiting a want of judgment or discretion;
      as, a foolish act.

   3. Absurd; ridiculous; despicable; contemptible.

            A foolish figure he must make.        --Prior.

   Syn: Absurd; shallow; shallow-brained; brainless; simple;
        irrational; unwise; imprudent; indiscreet; incautious;
        silly; ridiculous; vain; trifling; contemptible. See
        {Absurd}.

Source : WordNet®

foolish
     adj 1: devoid of good sense or judgment; "foolish remarks"; "a
            foolish decision" [ant: {wise}]
     2: having or revealing stupidity; "ridiculous anserine
        behavior"; "a dopey answer"; "a dopey kid"; "some fool
        idea about rewriting authors' books" [syn: {anserine}, {dopy},
         {dopey}, {goosey}, {goosy}, {gooselike}]