dampen vs muffle

dampen is not a noun while muffle is a noun.

Word	Noun	Adjective	Verb	Adverb
dampen	No	No	Yes	No
muffle	Yes	No	Yes	No

As verbs, dampen and muffle are synonyms defined as:

Other synonyms of dampen include damp, dull, mute, tone down.

dampen (noun)	muffle (noun)
	a kiln with an inner chamber for firing things at a low temperature

dampen (verb)	muffle (verb)
lessen in force or effect	suppress in order to conceal or hide
make moist	deaden (a sound or noise), especially by wrapping
check; keep in check (a fire)
make vague or obscure or make (an image) less visible
reduce the amplitude (of oscillations or waves)
suppress or constrain so as to lessen in intensity
deaden (a sound or noise), especially by wrapping