card index vs card catalog

card index and card catalog both are nouns.

Word	Noun	Adjective	Verb	Adverb
card index	Yes	No	No	No
card catalog	Yes	No	No	No

As nouns, card index and card catalog are synonyms defined as:

card index and card catalog: an alphabetical listing of items (e.g., books in a library) with a separate card for each item

Other synonyms of card index include card catalogue.

card index (noun)	card catalog (noun)
an alphabetical listing of items (e.g., books in a library) with a separate card for each item	an alphabetical listing of items (e.g., books in a library) with a separate card for each item
	a library catalog in which each publication is described on a separate file card