Lethal (adjective)

1. Causing death.
2. Capable of causing death.
3. Extremely harmful or dangerous.

Origin:

From middle english lethale, from old english lǣþe ("fatal"), from proto-germanic *laiþaz ("fatal"), from proto-indo-european *leyt- ("to die").

Examples:

1. The poison was lethal and killed the victim within minutes.
2. The virus is highly lethal and spreads rapidly.
3. The weapon was lethal enough to take out a tank.
4. The disease is lethal, with no known cure.
5. The drugs were lethal and caused many deaths.