tabu

1. taboo
   Novac je u mnogim porodicama i dalje tabu. — In many families money is still a taboo.
   Ova serija je srušila jedan veliki tabu. — This series broke a big taboo.

2. taboo
   Mentalno zdravlje više nije tabu tema. — Mental health is no longer a taboo subject.
   Kod nas je to i dalje tabu pitanje. — Here it's still a taboo question.

As an adjective it does not decline and usually comes before the noun: tabu tema, tabu temu.