rot vs moulder

rot is a noun but moulder is not a noun.

Word	Noun	Adjective	Verb	Adverb
rot	Yes	No	Yes	No
moulder	No	No	Yes	No

As verbs, rot and moulder are synonyms defined as:

Other synonyms of rot include decompose, molder.

rot (noun)	moulder (noun)
unacceptable behavior (especially ludicrously false statements)
(biology) the process of decay caused by bacterial or fungal action
a state of decay usually accompanied by an offensive odor

rot (verb)	moulder (verb)
become physically weaker	break down
break down