Source : Webster's Revised Unabridged Dictionary (1913)

Blissful \Bliss"ful\, a.
   Full of, characterized by, or causing, joy and felicity;
   happy in the highest degree. ``Blissful solitude.'' --Milton.
   -- {Bliss"ful*ly}, adv. -- {Bliss"ful*ness}, n.

Source : WordNet®

blissfulness
     n : a state of extreme happiness [syn: {bliss}, {cloud nine}, {seventh
         heaven}, {walking on air}]