There’s a big difference between a hand gesture, which has always had a vague meaning, and a word like fascism that has a discrete meaning. It’s meaning hasn’t changed; it’s just that some people are too lazy to use it properly or understand it.
Your “failure of a common definition” is an extension of the war against science. Just like “gravity”, fascism doesn’t give a shit if you believe in it, or if you are too lazy to give it the proper meaning. In the end, the result is the same whether you believe in it or not.
