An effect or situation that is lethally severe can cause serious harm or death. This word is often used to describe something that's extremely bad.
When someone says that a situation is "lethal," they usually mean it's so bad that it could be fatal. For example, if a person's health condition has become lethal, it means their life is in danger. If a virus is considered lethal, it can cause serious illness and potentially death. In this sense, lethal often describes something or someone that poses an extreme risk to human life.
In a lethal manner, in manner which is or will be fatal.
Example: He was lethally poisoned by the cobra and died a day later of it.
