Source : Webster's Revised Unabridged Dictionary (1913)

Winsome \Win"some\, a. [Compar. {Winsomer}; superl.
   {Winsomest}.] [AS. wynsum, fr. wynn joy; akin to OS. wunnia,
   OHG. wunna, wunni, G. wonne, Goth. wunan to rejoice (in
   unwunands sad), AS. wunian to dwell. ????. See {Win}, v. t.,
   {Wont}, a.]
   1. Cheerful; merry; gay; light-hearted.

            Misled by ill example, and a winsome nature.
                                                  --Jeffrey.

   2. Causing joy or pleasure; gladsome; pleasant.

            Still plotting how their hungry ear That winsome
            voice again might hear.               --Emerson.

Source : WordNet®

winsome
     adj : charming in a childlike or naive way