quantity vs copiousness

quantity and copiousness both are nouns.

Word	Noun	Adjective	Verb	Adverb
quantity	Yes	No	No	No
copiousness	Yes	No	No	No

As nouns, copiousness is a hyponym of quantity; that is, copiousness is a word with a more specific, narrower meaning than quantity:

Other hyponyms of quantity include abundance, teemingness.

quantity (noun)	copiousness (noun)
how much there is or how many there are of something that you can quantify	the property of a more than adequate quantity or supply
an adequate or large amount
the concept that something has a magnitude and can be represented in mathematical expressions by a constant or a variable