senescence

Senescence can be traced back to Latin senex, meaning "old." Can you guess which other English words come from senex? Senile might come to mind, as well as senior. But another one might surprise you: senate. This word for a legislative assembly dates back to ancient Rome, where the Senatus was originally a council of elders composed of the heads of patrician families. There's also the much rarer senectitude, which, like senescence, refers to the state of being old (specifically, to the final stage of the normal life span).