seafood vs periwinkle

seafood and periwinkle both are nouns.

Word	Noun	Adjective	Verb	Adverb
seafood	Yes	No	No	No
periwinkle	Yes	No	No	No

As nouns, periwinkle is a hyponym of seafood; that is, periwinkle is a word with a more specific, narrower meaning than seafood:

seafood: edible fish (broadly including freshwater fish) or shellfish or roe etc
periwinkle: small edible marine snail; steamed in wine or baked

seafood (noun)	periwinkle (noun)
edible fish (broadly including freshwater fish) or shellfish or roe etc	edible marine gastropod
	small edible marine snail; steamed in wine or baked
	chiefly trailing poisonous plants with blue flowers
	commonly cultivated Old World woody herb having large pinkish to red flowers