black rockweed vs tang

black rockweed and tang both are nouns.

Word	Noun	Adjective	Verb	Adverb
black rockweed	Yes	No	No	No
tang	Yes	No	No	No

As nouns, black rockweed and tang are synonyms defined as:

black rockweed and tang: a common rockweed used in preparing kelp and as manure

Other synonyms of black rockweed include bladder fucus, bladderwrack, Fucus vesiculosus.

black rockweed (noun)	tang (noun)
a common rockweed used in preparing kelp and as manure	any of various kelps especially of the genus Laminaria
	any of various coarse seaweeds
	brown algae seaweed with serrated edges
	a common rockweed used in preparing kelp and as manure
	a tart spicy quality
	the taste experience when a savoury condiment is taken into the mouth