fatal · mortal · deadly · to sacrifice one's life

To him this is a deadly blow.

The tip of the spear was dipped in a deadly poison.

You can't seriously expect that they won't recognize you in that disguise. That lopsided, dime store moustache is a dead giveaway!

Ebola is one of the most virulent viruses known to man.

So it seems that cloud of odorless deadly gas had a silver lining after all.