Source : Webster's Revised Unabridged Dictionary (1913)

Entertaining \En`ter*tain"ing\, a.
   Affording entertainment; pleasing; amusing; diverting. --
   {En`ter*tain"ing*ly}, adv. -- {En`ter*tain"ing*ness}, n.

Source : WordNet®

entertainingly
     adv : in an entertaining manner; "Byron's consumed memoirs
           possessed the merit of being well and entertainingly
           written"