Source : Webster's Revised Unabridged Dictionary (1913)

Dullness \Dull"ness\, n.
   The state of being dull; slowness; stupidity; heaviness;
   drowsiness; bluntness; obtuseness; dimness; want of luster;
   want of vividness, or of brightness. [Written also
   {dulness}.]

         And gentle dullness ever loves a joke.   --Pope.

Source : WordNet®

dulness
     n 1: the quality of being slow to understand [syn: {dullness}, {obtuseness}]
     2: the quality of lacking interestingness [syn: {dullness}]
     3: a lack of visual brightness [syn: {dullness}] [ant: {brightness}]
     4: without sharpness of edge or point [syn: {dullness}, {bluntness}]
        [ant: {asperity}, {sharpness}]