cost ledger vs account book

cost ledger and account book both are nouns.

Word	Noun	Adjective	Verb	Adverb
cost ledger	Yes	No	No	No
account book	Yes	No	No	No

As nouns, account book is a hypernym of cost ledger; that is, account book is a word with a broader meaning than cost ledger:

cost ledger: ledger showing the accumulated costs classified in various ways
account book: a record in which commercial accounts are recorded

Other hypernyms of cost ledger include book, book of account, ledger, leger.

cost ledger (noun)	account book (noun)
ledger showing the accumulated costs classified in various ways	a record in which commercial accounts are recorded