directory vs reference work

directory and reference work both are nouns.

Word	Noun	Adjective	Verb	Adverb
directory	Yes	No	No	No
reference work	Yes	No	No	No

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

Other hypernyms of directory include book of facts, reference, reference book.

directory (noun)	reference work (noun)
an alphabetical list of names and addresses	a book to which you can refer for authoritative facts
(computer science) a listing of the files stored in memory (usually on a hard disk)