seaweed vs sea wrack

seaweed and sea wrack both are nouns.

Word	Noun	Adjective	Verb	Adverb
seaweed	Yes	No	No	No
sea wrack	Yes	No	No	No

As nouns, sea wrack is a hyponym of seaweed; that is, sea wrack is a word with a more specific, narrower meaning than seaweed:

seaweed: plant growing in the sea, especially marine algae
sea wrack: growth of marine vegetation especially of the large forms such as rockweeds and kelp

Other hyponyms of seaweed include arame, wrack, seagrass, wrack, sea tang, tang.

seaweed (noun)	sea wrack (noun)
plant growing in the sea, especially marine algae	growth of marine vegetation especially of the large forms such as rockweeds and kelp
	submerged marine plant with very long narrow leaves found in abundance along North Atlantic coasts