1. without sharpness or clearness of edge or point

e.g. the dullness of the pencil made his writing illegible

Synonym: bluntness

2. lack of sensibility

e.g. there was a dullness in his heart
without him the dullness of her life crept into her work no matter how she tried to compartmentalize it.

3. a lack of visual brightness

e.g. the brightness of the orange sky was reflected in the dullness of the orange sea

4. the quality of lacking interestingness

e.g. the stories were of a dullness to bring a buffalo to its knees

5. the quality of being slow to understand

Synonym: obtuseness