Word eaters are shadows 'sent' to Hieron by the Heat and the Dark. Their name refers to a word eater's ability to consume language from the minds of others, removing people's ability to voice or envision concepts while the word eater itself can embody and distort that idea, turning it into a vicious thing.
Autumn in Hieron
“
They're shadows, you know. The word eaters? Sent to Hieron by the Nothing that came before. Heat and Dark that tear language whole from minds and culture, and replace it with void. When they attack openly, they're easy to deal with. But when they're coy, and subtle, they can erase whole civilizations. That's how they split the goblins and the elves, made them forget those old words. Trust. Friendship. The greater good an' all that. They stole other words, too. Warmth. Love. Coolness. And twisted them. Into their most extreme and dangerous forms.
So, in order to stop the word eaters and resume their journey east, the party tracked down Kindrali, only to find that the old ogre king had been killed and replaced by the leader of those shadows. And when they found it, it grinned the way murderers do. It toyed with them, like a large cat.”
The Ice Party encountered word eaters around the Mark of the Erasure, where the shadows had once destroyed the partnership between the snow elves and goblins of Auniq; most of the latter of which now roamed the area as a senseless horde called the Nameless. After meeting with Mee Kosh, an old goblin who had not lost his words, the party gained an idea of what had once happened there and went to find an Kindrali, He Who Remembers the Day, only to learn that he had been killed and impersonated by the word eaters' leader. However, Fantasmo vanquished the being by telling it of the ignorance that scared and motivated him into his life of learning; as it absorbed the concept of ignorance it lost the words it had stolen away.