dullness

noun

1.
the quality of being slow to understand
Derived from:
dull
2.
the quality of lacking interestingness
Derived from:
dull
3.
a lack of visual brightness
Antonym:
brightness
Derived from:
dull
4.
lack of sensibility
Derived from:
dull
5.
without sharpness or clearness of edge or point
Antonym:
sharpness
Derived from:
dull