earnest vs serious

earnest is a noun but serious is not a noun.

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

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

earnest (adjective)	serious (adjective)
not distracted by anything unrelated to the goal	concerned with work or important matters rather than play or trivialities
characterized by a firm and humorless belief in the validity of your opinions	completely lacking in playfulness
sincerely earnest	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