lustrum

noun

lus·​trum ˈlə-strəm 

plural lustrums or lustra ˈlə-strə 

1

: a period of five years

2

a

: a purification of the whole Roman people made in ancient times after the census every five years

b

: the Roman census

Word History

Etymology

Latin

First Known Use

1590, in the meaning defined at sense 1