fizzle out vs taper off

fizzle out and taper off both are verbs.

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

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

Other synonyms of fizzle out include fizzle, peter out.

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