copious vs voluminous

copious and voluminous both are adjectives.

Word	Noun	Adjective	Verb	Adverb
copious	No	Yes	No	No
voluminous	No	Yes	No	No

As adjectives, copious and voluminous are synonyms defined as:

copious and voluminous: large in number or quantity (especially of discourse)

copious (adjective)	voluminous (adjective)
affording an abundant supply	large in number or quantity (especially of discourse)
large in number or quantity (especially of discourse)	marked by repeated turns and bends
	large in volume or bulk