muffle vs bottle up

muffle is a noun but bottle up is not a noun.

Word	Noun	Adjective	Verb	Adverb
muffle	Yes	No	Yes	No
bottle up	No	No	Yes	No

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

muffle: suppress in order to conceal or hide
bottle up: consciously restrain from showing; of emotions, desires, impulses, or behavior

Other hypernyms of muffle include inhibit, suppress.

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

muffle (verb)	bottle up (verb)
suppress in order to conceal or hide	consciously restrain from showing; of emotions, desires, impulses, or behavior
deaden (a sound or noise), especially by wrapping