pocketbook vs softback book

pocketbook and softback book both are nouns.

Word	Noun	Adjective	Verb	Adverb
pocketbook	Yes	No	No	No
softback book	Yes	No	No	No

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

Other hypernyms of pocketbook include paper-back book, paperback, paperback book, soft-cover, soft-cover book, softback.

pocketbook (noun)	softback book (noun)
a container used for carrying money and small personal items or accessories (especially by women)	a book with paper covers
pocket-sized paperback book
a pocket-size case for holding papers and paper money
your personal financial means