cousin-german vs first cousin

cousin-german and first cousin both are nouns.

Word	Noun	Adjective	Verb	Adverb
cousin-german	Yes	No	No	No
first cousin	Yes	No	No	No

As nouns, cousin-german and first cousin are synonyms defined as:

Other synonyms of cousin-german include cousin, full cousin.

cousin-german (noun)	first cousin (noun)
the child of your aunt or uncle	the child of your aunt or uncle