Forbidden is used to describe things that people strongly disapprove of or feel guilty about, and that are not often mentioned or talked about.
双语例句
例： The war was a forbidden subject.
这场战争是一个忌讳的话题。
例： Men fantasize as a substitute for acting out forbidden desires.
人类幻想是一种宣泄压抑禁欲的替代方式。