impost vs duty

impost and duty both are nouns.

Word	Noun	Adjective	Verb	Adverb
impost	Yes	No	No	No
duty	Yes	No	No	No

As nouns, duty is a hypernym of impost; that is, duty is a word with a broader meaning than impost:

Other hypernyms of impost include tariff.

impost (noun)	duty (noun)
the lowest stone in an arch -- from which it springs	the social force that binds you to the courses of action demanded by that force
money collected under a tariff	work that you are obliged to perform for moral or legal reasons
	a government tax on imports or exports