thanatos

At its core this word names the end of life, the moment breath and body part ways. The New Testament uses it for that plain fact again and again, from Jesus sorrowful "to the point of death" in Gethsemane to the believer staying faithful even if it costs his life.

But the writers also let the word grow. The same death that ends the body becomes, in their hands, a sentence a court can pronounce, a doom that sin earns, and finally a tyrant who has reigned over the whole human race since Adam. Paul can speak of death "reigning" and being the "last enemy," and Revelation can give Death a name and a horse to ride.

These are not separate words but one word stretched across a single idea: life cut off. Physical dying is the visible edge of it; the deeper New Testament claim is that this same death is a hostile power answering to sin, and that Christ has broken its hold. The senses below mark where the word stays literal, where it turns to a legal verdict, where it reaches for a ruin beyond the grave, and where it stands up as a personified enemy.

In a handful of places, mostly in Revelation, the word does not mean dying in general but a specific killing scourge: plague or pestilence. This use comes straight from the Greek Old Testament, where this same word regularly translated the Hebrew term for pestilence and stood beside sword and famine as one of God's instruments of judgment.

Revelation keeps that older pairing alive. Death rides out to kill "with sword and famine and plague," and the fall of Babylon comes in "plague and mourning and famine." Here the word is one disaster among several, which is the clue that it has narrowed from death-in-general to a single deadly blow.