stick-in-the-mud vs plodder

stick-in-the-mud and plodder both are nouns.

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

As nouns, stick-in-the-mud and plodder are synonyms defined as:

Other synonyms of stick-in-the-mud include slowcoach, slowpoke.

stick-in-the-mud (noun)	plodder (noun)
someone who moves slowly	someone who moves slowly
	someone who works slowly and monotonously for long hours
	someone who walks in a laborious heavy-footed manner

stick-in-the-mud (adjective)	plodder (adjective)
(used pejoratively) out of fashion; old fashioned