The fact of something being lethal; the ability of something to kill.
The degree of lethal (mortal) danger that something (usually a disease or a weapon) presents; the magnitude of its power to kill organisms exposed to it; this property is indirectly measured by any of various proxy rates, including mortality rate, case fatality rate, or infection fatality rate (for diseases) or kill rate (for weapons, pesticides, or parasites).
Death, the Grim Reaper or angel of death; and one of the Four Horsemen of the Apocalypse.