soften vs muffle

soften is not a noun while muffle is a noun.

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

As verbs, muffle is a hyponym of soften; that is, muffle is a word with a more specific, narrower meaning than soften:

Other hyponyms of soften include damp, dampen, dull, mute, tone down.

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

soften (verb)	muffle (verb)
become soft or softer	suppress in order to conceal or hide
make soft or softer	deaden (a sound or noise), especially by wrapping
lessen in force or effect
make less severe or harsh
protect from impact
make (images or sounds) soft or softer
give in, as to influence or pressure