There are lots of words that I don't know how to taboo, because I only have a partial and largely intuitive understanding of the concepts I'm referring to by them, and can't fully explain those concepts. Examples: "exist", "truth", "correct", "right", "moral", "rational", "should", "mathematical". I don't think anyone has asked me directly to taboo any of these words, but if someone did, I might ignore the request because I think my time could be better spent trying to communicate with others who seem to already share my understandings of these words.

In the case of "exist", I think that something exists implies that I can care about it and not be irrational. ("care about": for example, have a term for it in my utility function) This seems to at least capture a large part of what I mean when I say something exists, but I'm not sure if "exists" just means (something like) the correct decision theory allows a utility function to have a term for something, or if existence is somehow more fundamental than that and our ability to rationally care about something derives from its existence in that more fundamental sense. Does this make sense?

ETA: See also this relevant post.