It is the only word that the Raven knows how to say.
"Nevermore", perhaps? It's not clear exactly what you're asking about, but in the E.A. Poe poem "The Raven," "Nevermore" is the raven's response to all the narrator's statements or queries.
one is exhaustive
ONCE upon a midnight dreary, while I pondered weak and weary,
The raven is almost always a symbol of death. In this poem, it symbolizes the devil or a demon.