blue book vs directory

blue book and directory both are nouns.

Word	Noun	Adjective	Verb	Adverb
blue book	Yes	No	No	No
directory	Yes	No	No	No

As nouns, directory is a hypernym of blue book; that is, directory is a word with a broader meaning than blue book:

blue book (noun)	directory (noun)
a register of persons who are socially prominent	an alphabetical list of names and addresses
a report published by the British government; bound in blue	(computer science) a listing of the files stored in memory (usually on a hard disk)
a blue booklet used in universities for writing examinations