Débil, Spanish for “weak,” comes from the same root as the English word debilitating: the Latin debilitas, meaning the same. This is another “obvious once you know” etymology.

Curiously, debilitas itself comes from the prefix de- (“away from”) and the Proto-Indo-European root *bel‑, meaning “strong.” From the same root we get, via other routes, the strong men of the Bolsheviks. Yes, it’s the same b‑l root there too!