serious vs playfulness

serious is not a noun while playfulness is a noun.

Word	Noun	Adjective	Verb	Adverb
serious	No	Yes	No	No
playfulness	Yes	No	No	No

serious (noun)	playfulness (noun)
	activities that are enjoyable or amusing
	a disposition to find (or make) causes for amusement
	a festive merry feeling

serious (adjective)	playfulness (adjective)
concerned with work or important matters rather than play or trivialities
completely lacking in playfulness
causing fear or anxiety by threatening great harm
requiring effort or concentration; complex and not easy to answer or solve
of great consequence
appealing to the mind