largeness vs magnitude

largeness and magnitude both are nouns.

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

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

largeness (noun)	magnitude (noun)
the property of having a relatively great size	the property of relative size or extent (whether large or small)
large or extensive in breadth or importance or comprehensiveness	relative importance
the quality of being pretentious (behaving or speaking in such a manner as to create a false appearance of great importance or worth)	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
the capacity to understand a broad range of topics