The verb σηπω (sepo) means to rot or be putrid: to be slowly digested by an infection of bacteria and fungi and be reduced to dust. In the classics, this verb occurs mostly in the passive form, and often used to describe infected and thus rotting flesh, dead or living (hence our English term septic). It's thought to stem from a noun σηψ (seps), which rather specifically described a putrefying wound inflicted by a serpent.

It's formally not clear whether these words are Indo-European or not, but here at Abarim Publications we're rather struck by their similarities to the Hebrew root ספף (sapap), to make or mark a threshold (which something that's rotting has obviously crossed). Verb שוף (shup) means to violate in the sense of illicitly entering one's personal space (or body). This verb became associated with the bite of a snake, and the noun שפיפן (shepipon) denotes a kind of snake.

Our verb σηπω (sepo) is used in James 5:2 only, but from it derives: