solemn vs sincere

solemn and sincere both are adjectives.

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

As adjectives, solemn and sincere are synonyms defined as:

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

Other synonyms of solemn include earnest.

solemn (adjective)	sincere (adjective)
dignified and somber in manner or character and committed to keeping promises	open and genuine; not deceitful
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