Book vs Good Book

Book and Good Book both are nouns.

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

As nouns, Book and Good Book are synonyms defined as:

Other synonyms of Book include Bible, Christian Bible, Holy Scripture, Holy Writ, Scripture, Word, Word of God.

Book (noun)	Good Book (noun)
the sacred writings of the Christian religions	the sacred writings of the Christian religions
the sacred writings of Islam revealed by God to the prophet Muhammad during his life at Mecca and Medina