solemn vs earnest

solemn is not a noun while earnest is a noun.

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

As adjectives, solemn and earnest are synonyms defined as:

solemn and earnest: characterized by a firm and humorless belief in the validity of your opinions

Other synonyms of solemn include sincere.

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

solemn (adjective)	earnest (adjective)
dignified and somber in manner or character and committed to keeping promises	not distracted by anything unrelated to the goal
characterized by a firm and humorless belief in the validity of your opinions	characterized by a firm and humorless belief in the validity of your opinions
	sincerely earnest