cargo ships vs merchant vessels

cargo ships and merchant vessels both are nouns.

Word	Noun	Adjective	Verb	Adverb
cargo ships	Yes	No	No	No
merchant vessels	Yes	No	No	No

As nouns, cargo ships and merchant vessels are synonyms defined as:

cargo ships and merchant vessels: conveyance provided by the ships belonging to one country or industry

Other synonyms of cargo ships include merchant marine, shipping.

cargo ships (noun)	merchant vessels (noun)
conveyance provided by the ships belonging to one country or industry	conveyance provided by the ships belonging to one country or industry