frivolity
fri-vol-i-ty
noun
The quality of being light-hearted and not serious, often inappropriately so.
"Their office was known for its occasional frivolity."
Thesaurus
Synonyms: fluff, frippery, bagatelle, frivolousness, clowning, japery, prank, harlequinade, buffoonery
Antonyms: earnestness, serious-mindedness, seriousness, sincerity