Erosion of Definition

The act of altering or "eroding" the definition of a word or term so that it no longer means anything useful (or what the person using the term intended it to mean), thereby making the original and intended topic difficult or even impossible to discuss in any meaningful manner. This fallacy can be a diversion, or it can be used to pre-emptively silence legitimate questions and criticism that the person does not want to deal with.

Basically, it runs like this: "You are using (insert word or term) to describe something. But the word/term you are using actually means X. But X does not exist/is not an issue. Therefore, you are not bringing up a valid or real issue."

For example, Sadie asks Clara if she thinks that aliens will ever attack Earth. Clara responds, "We are all children of the Universe, which means that none of us are really 'aliens.' So no, you will never have to worry about aliens attacking Earth." Thus Clara dodges Sadie's actual question while rendering a key term meaningless, making it that much harder for Sadie to effectively express herself in the future.

Or, Mark is sitting on a bench looking glum. Jim walks up to him and asks him what's wrong. Mark explains that his friend Patty hurt herself in a skiing accident and that she's stuck in the hospital. Jim responds, "No, she didn't. Patty didn't hurt herself." Mark asks him what he means. "The 'self' is only an illusion, so there is no 'self' to hurt. Therefore, you don't need to feel bad about Patty hurting herself."

If you think you've spotted this fallacy, be careful that you are not committing the Origin Fallacy! This fallacy isn't simply about words gaining new meanings - it's when they're redefined in such a way that constricts or restricts a person's ability to communicate or even conceptualize a particular concept.