Guiltythree
Based off the descriptions given about the NCs, I’d imagine that defilement, unlike corruption, is a specific method of involved with the truth hidden in this river and the process of keeping it unknown. A witness “sees the truth” to which the defiled witness has its eyes removed and a herald “speaks the truth” to which their mouths were sewn shut. The Seeker looks for truth to which the defiled seeker hides/kills the truth (behind a cloud poison/toxin.) This defilement revolves around keeping truth secret or maybe the truth destroying them 🤔
Defilement could just be the same as corruption as it literally means losing purity/falling from grace, and that was what happened to the old snake. It's just that they might have different mediums in infecting a creature. It's possible that the corruption that we are familiar with infects physically like what happened to Weaver's arm while the defilement inside the tomb could be something that sprouts from your soul core/soul sea, something similar to how a sleeper would turn into a monster.