different between dullness vs inactivity

English

From dull +? -ness.

dullness (usually uncountable, plural dullnesses)

The quality of being slow of understanding things; stupidity.
The quality of being uninteresting; boring or irksome.
Lack of interest or excitement.
The lack of visual brilliance; want of sheen.
(of an edge) bluntness.
The quality of not perceiving or kenning things distinctly.
(archaic) Drowsiness.
- c. 1610-11, William Shakespeare, The Tempest, Act I scene ii^[1]:
  Prospero: […] Thou art inclin'd to sleep. 'Tis a good dulness, / And give it way— I know thou canst not choose.

From in- +? activity.

inactivity (countable and uncountable, plural inactivities)

The quality of being inactive; idleness; passiveness.
- 1994, Helene Barbara Weinberg, Doreen Bolger, David Park Curry, American Impressionism and Realism
  Painters depicted Idle Hours (see fig. 99), reverie, solitude, and other themes that reflected Americans' new willingness to eschew productivity, and they sold their canvases to patrons who enjoyed both the inactivities portrayed and seeing themselves portrayed in inactivities.

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