Something that is iniquitous is extremely immoral or wicked, such as an iniquitous political regime that assassinates its enemies.
Use the adjective iniquitous to describe something that is truly bad, morally wrong, extremely wicked, or completely unfair. It’s a strong word — don't use it lightly. If you go see a movie that’s boring and too long, for example, it’s just a bad movie. But a movie that encourages people to take violent action against a minority group? That's iniquitous because the movie's message is grossly immoral.