tabu vs forbidden

tabu is a noun but forbidden is not a noun.

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

As adjectives, tabu and forbidden are synonyms defined as:

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

tabu (noun)	forbidden (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

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