chauvinist

The word traces back to chauvinism, formed from a personal name. It is a piecewise doublet of "Calvinist," meaning both words descend from different forms of the same underlying name.

The facts given don't trace a shift in meaning over time, so the honest story here is simply the name-based origin itself, split into two different words that grew apart in use.

It's a doublet of "Calvinist" — the two words come from different forms of the same original name, making them unexpected linguistic siblings.