voucher vs book token

voucher and book token both are nouns.

Word	Noun	Adjective	Verb	Adverb
voucher	Yes	No	No	No
book token	Yes	No	No	No

As nouns, book token is a hyponym of voucher; that is, book token is a word with a more specific, narrower meaning than voucher:

voucher: a negotiable certificate that can be detached and redeemed as needed
book token: a gift voucher that can be exchanged for books costing up to an amount given on the voucher

Other hyponyms of voucher include luncheon voucher, meal ticket, twofer.

voucher (noun)	book token (noun)
a negotiable certificate that can be detached and redeemed as needed	a gift voucher that can be exchanged for books costing up to an amount given on the voucher
a document that serves as evidence of some expenditure
someone who vouches for another or for the correctness of a statement