merchant marine vs conveyance

merchant marine and conveyance both are nouns.

Word	Noun	Adjective	Verb	Adverb
merchant marine	Yes	No	No	No
conveyance	Yes	No	No	No

As nouns, conveyance is a hypernym of merchant marine; that is, conveyance is a word with a broader meaning than merchant marine:

merchant marine: conveyance provided by the ships belonging to one country or industry
conveyance: something that serves as a means of transportation

Other hypernyms of merchant marine include transport.

merchant marine (noun)	conveyance (noun)
conveyance provided by the ships belonging to one country or industry	act of transferring property title from one person to another
the crew of a merchant vessel	the act of moving something from one location to another
	something that serves as a means of transportation
	the transmission of information
	document effecting a property transfer