omnicide

As a letter s

is the letter s with a.

As a noun omnicide is

the total extinction of the human species as a result of human action most commonly it refers to human extinction through nuclear warfare, but it can also refer to such extinction through other means such as global anthropogenic ecological catastrophe.

As nouns the difference between omnicide and ethnocide

is that omnicide is the total extinction of the human species as a result of human action most commonly it refers to human extinction through nuclear warfare, but it can also refer to such extinction through other means such as global anthropogenic ecological catastrophe while ethnocide is the deliberate and systematic destruction of an ethnic group, accomplished either by destroying the members of the group (genocide) or by destroying its cultural identity (culturcide).