A substance that is lethal can kill people or animals.
a lethal dose of sleeping pills.
致命剂量的安眠药。
If you describe something as lethal, you mean that it is capable of causing a lot of damage.
Amorality and intelligence is probably the most lethal combination to be found within one personality.
聪明而缺乏道德感可能是危害最大的性格组合。