lustrum

[luhs-truh m] /ˈlʌs trəm/
noun, plural lustrums, lustra
[luhs-truh] /ˈlʌs trə/ (Show IPA)
1.
Also, luster; especially British, lustre. a period of five years.
2.
Roman History. a lustration or ceremonial purification of the people, performed every five years, after the taking of the census.
Origin
1580-90; < Latin lūstrum; cf. luster1
Examples from the web for lustrum
  • Neither a century nor a lustrum is typically graced with any special moniker.
British Dictionary definitions for lustrum

lustrum

/ˈlʌstrəm/
noun (pl) -trums, -tra (-trə)
1.
a period of five years
Word Origin
C16: from Latin: ceremony of purification, from lustrāre to brighten, purify
Word Origin and History for lustrum
n.

(plural lustra), "purification of the Roman people every five years," 1580s, from Latin lustrum, perhaps from root of luere "to wash," related to lavere (see lave). Or [Watkins, Klein] from PIE *leuk-stro-, from base *leuk- "light, brightness."