Good Book vs Old Testament

Good Book and Old Testament both are nouns.

Word	Noun	Adjective	Verb	Adverb
Good Book	Yes	No	No	No
Old Testament	Yes	No	No	No

Good Book (noun)	Old Testament (noun)
the sacred writings of the Christian religions	the collection of books comprising the sacred scripture of the Hebrews and recording their history as the chosen people; the first half of the Christian Bible