softback vs pocketbook

softback and pocketbook both are nouns.

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

As nouns, pocketbook is a hyponym of softback; that is, pocketbook is a word with a more specific, narrower meaning than softback:

Other hyponyms of softback include pocket book, pocket edition.

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