levity

noun

1. (uncountable, usually)A lightness of manner or speech, frivolity; flippancy; a lack of appropriate seriousness; an inclination to make a joke of serious matters.

   “An attempt to inject a little levity into the proceedings.”

2. (obsolete, uncountable, usually)A lack of steadiness.
3. (uncountable, usually)The state or quality of being light, buoyancy.

   “Most of the confidences were unsought - frequently I have feigned sleep, preoccupation or a hostile levity […]”

   “[…]it would really seem as if there was something nomadic in our natures, a principle of levity and restlessness […]”

   “Hydrogen […] rises in the air on account of its levity.”

4. (countable, usually)A lighthearted or frivolous act.

   “For though it be something wonderful to tell that any should have hearts so hardened, in the midst of such a calamity, as to rob and steal, yet certain it is that all sorts of villainies, and even levities and debaucheries, were then practiced in the town as openly as ever: I will not say quite as frequently, because the number of people were many ways lessened.”

   “[…] or do the people joy less than common in their levities?"”

   “His incorrigible levities had probably lost him the countenance of most of his more serious acquaintances[…”