serious vs unplayful

serious and unplayful both are adjectives.

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

As adjectives, serious and unplayful are synonyms defined as:

Other synonyms of serious include sober.

serious (adjective)	unplayful (adjective)
concerned with work or important matters rather than play or trivialities	completely lacking in playfulness
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