numerousness vs multiplicity

numerousness and multiplicity both are nouns.

Word	Noun	Adjective	Verb	Adverb
numerousness	Yes	No	No	No
multiplicity	Yes	No	No	No

As nouns, numerousness and multiplicity are synonyms defined as:

Other synonyms of numerousness include numerosity.

numerousness (noun)	multiplicity (noun)
a large number	a large number
	the property of being multiple