Source : Webster's Revised Unabridged Dictionary (1913)

Facetious \Fa*ce"tious\, a. [Cf. F. fac['e]tieux. See
   {Faceti[ae]}.]
   1. Given to wit and good humor; merry; sportive; jocular; as,
      a facetious companion.

   2. Characterized by wit and pleasantry; exciting laughter;
      as, a facetious story or reply. -- {Fa*ce"tious*ly}, adv.
      -- {Fa*ce"tious*ness}, n.

Source : WordNet®

facetiousness
     n : playful humor