fizzle out vs fizzle

fizzle out is not a noun while fizzle is a noun.

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

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

Other synonyms of fizzle out include peter out, taper off.

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

fizzle out (verb)	fizzle (verb)
end weakly	end weakly