multiplicity vs magnitude

multiplicity and magnitude both are nouns.

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

As nouns, magnitude is a hypernym of multiplicity; that is, magnitude is a word with a broader meaning than multiplicity:

multiplicity (noun)	magnitude (noun)
a large number	the property of relative size or extent (whether large or small)
the property of being multiple	relative importance
	a number assigned to the ratio of two quantities; two quantities are of the same order of magnitude if one is less than 10 times as large as the other; the number of magnitudes that the quantities differ is specified to within a power of 10