People who are suicidal want to kill themselves or are in a mental state in which it is likely that they will try to do so.

Pete was so depressed after his girlfriend left him that I actually thought he was suicidal. 皮特自女朋友离开后情绪就非常低落，实际上，我认为他有自杀倾向。

Suicidal behaviour is likely to result in death.

He took some suicidal risks. 他冒了很大的险，几乎是玩儿命。

causing your own defeat or failure

It would be suicidal to say that in a job interview. 在工作面试的时候说那些话就是自断前程。