phthora

This is the word's home ground. It names what happens to anything made of matter: food goes off, bodies wear out, the whole living world runs down toward death. It is not a judgment on the thing that decays, only a description of how physical existence works.

Paul builds his case for the resurrection on exactly this. A body goes into the ground the way a seed does, subject to rot, and comes up in a state that cannot rot at all. He can even use the word for the perishable itself, as a name for everything on the decaying side of that line, and he says flatly that it cannot inherit what will not decay. In Romans he widens the picture past human bodies: the whole created world is held in a slavery to running down that it will one day be released from.

At the plainest end, the word can describe household goods simply being used up. Food and drink go into a person and are gone; rules built on which of them you may touch are rules about things already on their way to the rubbish heap.

The verb behind it (φθείρω) covers the same ground as an action, and there is a strengthened relative (διαφθορά) that narrows in on one thing only, the rotting of a corpse in the grave.

Here the word names an end rather than a process. Something is not slowly wearing down; it is wiped out. Second Peter uses it of animals bred to be trapped and killed, and the point of the comparison is brutal: the men he is attacking are headed for the same finish, and by the same reflex that makes an animal walk into a snare.

Paul's harvest image in Galatians works the same way. A life spent feeding your own appetites brings in a crop, and the crop is ruin, set directly against the everlasting life that the other kind of sowing brings in.

The overlap with the ordinary Greek word for destruction (ἀπώλεια) is real, but this word keeps a flavor that word does not: the ruin it names is of a piece with rotting. What is destroyed here is not simply switched off; it goes the way everything perishable goes.

The physical picture carries over to character. A person can go bad the way meat goes bad, and Second Peter uses the word for exactly that: a rot loose in the world, driven by appetite, which the promises of God let a person get clear of.

What makes this more than name-calling is the enslaving power the word carries here. The men Peter attacks are advertising freedom while they themselves are owned by the very rot they peddle, because whatever beats you becomes your master. Rot is not just a stain on them; it is who holds the leash.

The main Hebrew word for this in the Old Testament (שָׁחַת) works the same way, fusing moral corruption with the wreckage it invites, most famously when all flesh had ruined its way before the flood.