serious vs earnest

serious is not a noun while earnest is a noun.

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

serious (noun)	earnest (noun)
	something of value given by one person to another to bind a contract

serious (adjective)	earnest (adjective)
concerned with work or important matters rather than play or trivialities	not distracted by anything unrelated to the goal
completely lacking in playfulness	characterized by a firm and humorless belief in the validity of your opinions
causing fear or anxiety by threatening great harm	sincerely earnest
requiring effort or concentration; complex and not easy to answer or solve
of great consequence
appealing to the mind