stick-in-the-mud vs mossy

stick-in-the-mud is a noun but mossy is not a noun.

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

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

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

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

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

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