"Thunder mugs" is an informal slang term that refers to chamber pots, which were used in the past as indoor toilets. The origins of the term are unclear but it may have been a reference to the loud noise produced when using the pot. Today, the term is rarely used, but there are several synonyms that can be used instead such as, chamber pot, bedpan, pot de chambre, slipper pan or piss pot. While these terms may not be as colorful as "thunder mugs," they are more widely recognized and less likely to cause confusion or offense.