Antonyms of noun seriousness

1 of 3 senses of seriousness

Sense 3
seriousness, earnestness, serious-mindedness, sincerity -- (the trait of being serious; "a lack of solemnity is not necessarily a lack of seriousness"- Robert Rice)
       Antonym of frivolity (Sense 1)
      => frivolity, frivolousness -- (the trait of being frivolous; not serious or sensible)

Synonyms/Hypernyms (Ordered by Estimated Frequency) of noun seriousness

3 senses of seriousness

Sense 1
earnestness, seriousness, sincerity -- (an earnest and sincere feeling)
       => gravity, solemnity -- (a solemn and dignified feeling)

Sense 2
seriousness, distressfulness -- (the quality of arousing fear or distress; "he learned the seriousness of his illness")
       => badness, severity, severeness -- (used of the degree of something undesirable e.g. pain or weather)

Sense 3
seriousness, earnestness, serious-mindedness, sincerity -- (the trait of being serious; "a lack of solemnity is not necessarily a lack of seriousness"- Robert Rice)
       => trait -- (a distinguishing feature of your personal nature)