textbook vs casebook

textbook and casebook both are nouns.

Word	Noun	Adjective	Verb	Adverb
textbook	Yes	Yes	No	No
casebook	Yes	Yes	No	No

As adjectives, textbook and casebook are synonyms defined as:

textbook and casebook: according to or characteristic of a casebook or textbook; typical

textbook (noun)	casebook (noun)
a book prepared for use in schools or colleges	a book in which detailed written records of a case are kept and which are a source of information for subsequent work

textbook (adjective)	casebook (adjective)
according to or characteristic of a casebook or textbook; typical	according to or characteristic of a casebook or textbook; typical