The Spanish word 'peor' meaning 'worse' comes directly from the Latin word 'peior', which also meant 'worse'. This is a straightforward inheritance where both the meaning and form remained quite stable - the Latin 'peior' simply evolved into 'peor' as the language developed into Spanish, with the 'i' being dropped.

'Peor' is already one of the basic Spanish words as it is the comparative form of 'malo' (bad). You might see it in common phrases like 'peor que' (worse than) or 'el peor' (the worst).

While English 'worse' is not related to 'peor' (it comes from Germanic roots instead), you might encounter the Latin root 'peior' in some formal English words like 'deteriorate' (to make worse or become worse) and 'impair' (to weaken or damage), though these connections are more distant and went through French before entering English.