If you haven't read Eco's essay on ur-fascism, it's a good read: https://theanarchistlibrary.org/library/umberto-eco-ur-fascism

So we come to my second point. There was only one Nazism. We cannot label Franco’s hyper-Catholic Falangism as Nazism, since Nazism is fundamentally pagan, polytheistic, and anti-Christian. But the fascist game can be played in many forms, and the name of the game does not change. The notion of fascism is not unlike Wittgenstein’s notion of a game. A game can be either competitive or not, it can require some special skill or none, it can or cannot involve money. Games are different activities that display only some “family resemblance,” as Wittgenstein put it. Consider the following sequence:

1___2___3___4

abc bcd cde def

Suppose there is a series of political groups in which group one is characterized by the features abc, group two by the features bcd, and so on. Group two is similar to group one since they have two features in common; for the same reasons three is similar to two and four is similar to three. Notice that three is also similar to one (they have in common the feature c). The most curious case is presented by four, obviously similar to three and two, but with no feature in common with one. However, owing to the uninterrupted series of decreasing similarities between one and four, there remains, by a sort of illusory transitivity, a family resemblance between four and one.

Fascism became an all-purpose term because one can eliminate from a fascist regime one or more features, and it will still be recognizable as fascist. Take away imperialism from fascism and you still have Franco and Salazar. Take away colonialism and you still have the Balkan fascism of the Ustashes. Add to the Italian fascism a radical anti-capitalism (which never much fascinated Mussolini) and you have Ezra Pound. Add a cult of Celtic mythology and the Grail mysticism (completely alien to official fascism) and you have one of the most respected fascist gurus, Julius Evola.