Definition of "Dullness" :

noun: without sharpness or clearness of edge or point

"The dullness of the pencil made his writing illegible."

noun: lack of sensibility

"There was a dullness in his heart."

noun: a lack of visual brightness

"The brightness of the orange sky was reflected in the dullness of the orange sea."

noun: the quality of lacking interestingness

"The stories were of a dullness to bring a buffalo to its knees."

noun: the quality of being slow to understand