shipping vs merchant marine

shipping and merchant marine both are nouns.

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

As nouns, shipping and merchant marine are synonyms defined as:

shipping and merchant marine: conveyance provided by the ships belonging to one country or industry

Other synonyms of shipping include cargo ships, merchant vessels.

shipping (noun)	merchant marine (noun)
the commercial enterprise of moving goods and materials	conveyance provided by the ships belonging to one country or industry
conveyance provided by the ships belonging to one country or industry	the crew of a merchant vessel