vigilante

Borrowed from Spanish vigilante, meaning "watchman" or "guard," which traces back to Latin vigilans.

The word entered English as a direct borrowing from Spanish, keeping its sense of someone keeping watch, though it's since narrowed toward people who take on enforcement or justice without official authority.

It's a doublet of vigilant — both descend from the same Latin root, vigilans, one arriving through Spanish and one through a more direct path into English.