volume vs magnitude

volume and magnitude both are nouns.

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

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

volume (noun)	magnitude (noun)
physical objects consisting of a number of pages bound together	the property of relative size or extent (whether large or small)
the magnitude of sound (usually in a specified direction)	relative importance
the property of something that is great in magnitude	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
a publication that is one of a set of several similar publications
the amount of 3-dimensional space occupied by an object
a relative amount