Words do indeed have meanings, as I am well aware. They often have multiple and subtly nuanced meanings. Merriam-Webster defines one of the meanings of “existential” as “grounded in existence or the experience of existence”. Hence the philosophy of existentialism: “a philosophy that emphasizes individual existence, freedom and choice. It is the view that humans define their own meaning in life, and try to make rational decisions despite existing in an irrational universe.”
Sure, “existential threat” could be interpreted in a narrow sense to mean a threat to our very existence, and hence a discussion about the imminent extinction of homo sapiens. But as I said, this is not a very useful or interesting discussion. A much more productive discussion grounded in reality would be about which threats pose the greatest risks to the quality of our experience of life on earth as we know it. I think it’s increasingly clear that climate change is by far the greatest such threat.