earnest vs solemn

earnest is a noun but solemn is not a noun.

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

As adjectives, earnest and solemn are synonyms defined as:

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

Other synonyms of earnest include sincere.

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

earnest (adjective)	solemn (adjective)
not distracted by anything unrelated to the goal	dignified and somber in manner or character and committed to keeping promises
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