bluefin tuna vs horse mackerel

bluefin tuna and horse mackerel both are nouns.

Word	Noun	Adjective	Verb	Adverb
bluefin tuna	Yes	No	No	No
horse mackerel	Yes	No	No	No

As nouns, bluefin tuna and horse mackerel are synonyms defined as:

bluefin tuna and horse mackerel: largest tuna; to 1500 pounds; of mostly temperate seas: feed in polar regions but breed in tropics

Other synonyms of bluefin tuna include bluefin, Thunnus thynnus.

bluefin tuna (noun)	horse mackerel (noun)
largest tuna; to 1500 pounds; of mostly temperate seas: feed in polar regions but breed in tropics	a California food fish
flesh of very large tuna	large elongated compressed food fish of the Atlantic waters of Europe
	largest tuna; to 1500 pounds; of mostly temperate seas: feed in polar regions but breed in tropics