The fact of something being lethal; the ability of something to kill(noun)
The rate of death of organisms exposed to something(noun)
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Use "lethality" in a sentence
"As you pointed out, the extra lethality is not required!"
"While I have no issue with a hunter using his 7mm Magnum or even his .300 Magnum (of whatever type) to take his deer, I believe there is no difference in lethality between those rounds and a well-aimed accurate handloaded 7x57 Mauser (with any of the bullets and powder load mentioned above) out to 300+ yards on a heart-lung shot."
"If you run a bullet or an arrow through the chest of any animal and it goes through both lungs or the heart, there is zero difference in lethality!"