The Spanish word 'petaca', meaning 'case' or 'flask', comes from the Nahuatl (Aztec) word 'petlacalli', which literally meant 'box made of reed mat'. This Nahuatl word was a compound formed from 'petlatl' meaning 'reed mat' and 'calli' meaning 'house' or 'box'. When the word was borrowed into Spanish, it was simplified from 'petlacalli' to 'petaca' and came to specifically refer to a case or flask, rather than any general box made of reed mat material.

Since 'petaca' comes from Nahuatl rather than Latin or Greek, there aren't many etymologically related simpler Spanish words. This word entered Spanish directly during the colonial period in Mexico when Spanish speakers encountered Nahuatl-speaking peoples and their material culture.

There aren't any commonly used English words directly related to 'petaca', as this word comes from Nahuatl. However, English has borrowed the word as 'petaca' in some contexts, particularly in reference to certain types of cases or containers, though it's not widely used in everyday English.