import duty vs duty

import duty and duty both are nouns.

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

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

Other hypernyms of import duty include tariff.

import duty (noun)	duty (noun)
a duty imposed on imports	the social force that binds you to the courses of action demanded by that force
	work that you are obliged to perform for moral or legal reasons
	a government tax on imports or exports