lustra

/L AH1 S T R AH0/
noun
  1. 1

    A ceremonial purification of all the people, performed every five years after the taking of the census; a lustration.

  2. 2

    (by extension) A period of five years.

Source: https://en.wiktionary.org/wiki/lustra, https://en.wiktionary.org/wiki/lustrum