tabu vs impermissible

tabu is a noun but impermissible is not a noun.

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

tabu (noun)	impermissible (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)	impermissible (adjective)
excluded from use or mention	not permitted
forbidden to profane use especially in South Pacific islands	not allowable