fizzle vs taper off

fizzle is a noun but taper off is not a noun.

Word	Noun	Adjective	Verb	Adverb
fizzle	Yes	No	Yes	No
taper off	No	No	Yes	No

As verbs, fizzle and taper off are synonyms defined as:

Other synonyms of fizzle include fizzle out, peter out.

fizzle (noun)	taper off (noun)
a complete failure
a fricative sound (especially as an expression of disapproval)

fizzle (verb)	taper off (verb)
end weakly	become smaller or less active
	end weakly