ship money vs customs duty

ship money and customs duty both are nouns.

Word	Noun	Adjective	Verb	Adverb
ship money	Yes	No	No	No
customs duty	Yes	No	No	No

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

ship money: an impost levied in England to provide money for ships for national defense
customs duty: money collected under a tariff

Other hypernyms of ship money include custom, customs, impost.

ship money (noun)	customs duty (noun)
an impost levied in England to provide money for ships for national defense	money collected under a tariff