Definition of levity:

a manner lacking seriousness

Synonyms of levity:

frivolity, flippancy, lightness, flightiness, giddiness, buoyancy, facetiousness, mirth, amusement, jocularity, humor

Opposite/Antonyms of levity:

permanence, seriousness, gravity, earnestness, solemnity, soberness, depression, heaviness, gloominess

Sentence/Example of levity:

The company encourages a little levity to make crammed flights slightly more tolerable.