Source : Webster's Revised Unabridged Dictionary (1913)

Blitheness \Blithe"ness\, n.
   The state of being blithe. --Chaucer.

Source : WordNet®

blitheness
     n : a feeling of spontaneous good spirits; "his cheerfulness
         made everyone feel better" [syn: {cheerfulness}] [ant: {cheerlessness}]