different between staidness vs serenity

English

staid +? -ness

staidness (usually uncountable, plural staidnesses)

The state or characteristic of being staid.
- 1836, Charles Dickens, Sketches of Boz, ch. 7:
  It is difficult to say whether Mr. John Dounce's red countenance, illuminated as it was by the flickering gas-light in the window before which he paused, excited the lady's risibility, or whether a natural exuberance of animal spirits proved too much for that staidness of demeanour which the forms of society rather dictatorially prescribe.
- 1887, Charlotte M. Yonge, Under the Storm, ch. 22:
  [T]here was a staidness and sobriety about her demeanour that kept all impertinence at a distance.

From Middle English serenyte, from Old French serenité, from Latin ser?nit?s, equivalent to serene +? -ity.

serenity (countable and uncountable, plural serenities)

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