stick-in-the-mud vs moss-grown

stick-in-the-mud is a noun but moss-grown is not a noun.

Word	Noun	Adjective	Verb	Adverb
stick-in-the-mud	Yes	Yes	No	No
moss-grown	No	Yes	No	No

As adjectives, stick-in-the-mud and moss-grown are synonyms defined as:

stick-in-the-mud and moss-grown: (used pejoratively) out of fashion; old fashioned

Other synonyms of stick-in-the-mud include fogyish, mossy, stodgy.

stick-in-the-mud (noun)	moss-grown (noun)
someone who moves slowly

stick-in-the-mud (adjective)	moss-grown (adjective)
(used pejoratively) out of fashion; old fashioned	overgrown with moss
	(used pejoratively) out of fashion; old fashioned