comic vs mirthful

comic is a noun but mirthful is not a noun.

Word	Noun	Adjective	Verb	Adverb
comic	Yes	Yes	No	No
mirthful	No	Yes	No	No

As adjectives, comic and mirthful are synonyms defined as:

Other synonyms of comic include amusing, comical, funny, laughable, risible.

comic (noun)	mirthful (noun)
a professional performer who tells jokes and performs comical acts

comic (adjective)	mirthful (adjective)
of or relating to or characteristic of comedy	arousing or provoking laughter
arousing or provoking laughter	full of or showing high-spirited merriment