muffle vs soften

muffle is a noun but soften is not a noun.

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

As verbs, soften is a hypernym of muffle; that is, soften is a word with a broader meaning than muffle:

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

muffle (verb)	soften (verb)
suppress in order to conceal or hide	become soft or softer
deaden (a sound or noise), especially by wrapping	make soft or softer
	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