Source : Webster's Revised Unabridged Dictionary (1913)

Fun \Fun\, n. [Perh. of Celtic origin; cf. Ir. & Gael. fonn
   pleasure.]
   Sport; merriment; frolicsome amusement. ``Oddity, frolic, and
   fun.'' --Goldsmith.

   {To make fan of}, to hold up to, or turn into, ridicule.