When something is prohibited, it's not allowed. If you see the sign "Swimming is prohibited," stay out of the water.
Whether used as a verb ("You prohibited your friend from entering") or an adjective ("The prohibited word escaped your lips"), prohibited means something was forbidden — a no-no. You often see it in signs like "Smoking prohibited." It's a strong word, indicating that something is banned and suggesting dire consequences if the ban is not obeyed. On the other hand, when something is prohibited it might seem more appealing.