proscribed vs tabu

proscribed is not a noun while tabu is a noun.

Word	Noun	Adjective	Verb	Adverb
proscribed	No	Yes	No	No
tabu	Yes	Yes	No	No

As adjectives, proscribed and tabu are synonyms defined as:

Other synonyms of proscribed include forbidden, out, prohibited, taboo, verboten.

proscribed (noun)	tabu (noun)
	an inhibition or ban resulting from social custom or emotional aversion
	a prejudice (especially in Polynesia and other South Pacific islands) that prohibits the use or mention of something because of its sacred nature

proscribed (adjective)	tabu (adjective)
excluded from use or mention	excluded from use or mention
	forbidden to profane use especially in South Pacific islands