Good Book vs Book

Good Book and Book both are nouns.

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

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

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

Good Book (noun)	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