Your dictionary editor gets to do that. That narrow definition you quote did not come out of thin air. Or maybe it did.

I’ve never heard of ‘fascisti’ - that’s just Italian for “fascists”, not an Organization.

There is a lot more nuance to what the word came to mean that is impossible to capture in one or two paragraphs. The Wikipedia page is already a great improvement over that, recommend that as a source instead, collectively reviewed by hundreds of editors.