Fromfrivolous +‎-ness.

frivolousness (countable anduncountable,pluralfrivolousnesses)

1. (uncountable) The quality of beingfrivolous.
   • 2016,Zadie Smith,Swing Time, New York, N.Y.:Penguin Press,→ISBN,page150:

     I felt, as usual, my own smallness next to her, the scale of what she had achieved, thefrivolousness of my own occupation in comparison, despite all she’d tried to direct me towards.

2. (countable) The result of beingfrivolous.

• frivolity
• frivolosity

• English terms suffixed with -ness
• English lemmas
• English nouns
• English uncountable nouns
• English countable nouns
• English terms with quotations

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