levity

plural levities

1. uncountableusuallyA 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.

   Antonyms: gravity

2. obsoleteuncountableusuallyA lack of steadiness.
3. uncountableusuallyThe state or quality of being light, buoyancy.

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

   1869, Mary Somerville, On Molecular and Microscopic Science, 1.1.12

   2 more examples

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

   1925, F[rancis] Scott Fitzgerald, The Great Gatsby, New York, N.Y.: Charles Scribner’s Sons, published 1953, →ISBN

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

   1838, Robert Montgomery Bird, Peter Pilgrim

4. countableusuallyA lighthearted or frivolous act.

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

   1872, J. Fenimore Cooper, The Bravo

   2 more examples

   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.

   1665, Daniel Defoe, A Journal of the Plague Year, Gutenberg

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

   1882, H.D. Traill, Sterne