Source : Webster's Revised Unabridged Dictionary (1913)

Obtuseness \Ob*tuse"ness\, n.
   State or quality of being obtuse.

Source : WordNet®

obtuseness
     n 1: the quality of being slow to understand [syn: {dullness}, {dulness}]
     2: the quality of lacking a sharp edge or point [ant: {acuteness}]