/lus"treuhm/ , n. , pl. lustrums, lustra /-treuh/ .
1. Also, luster; esp. Brit., lustre . a period of five years.
2. Rom. Hist. a lustration or ceremonial purification of the people, performed every five years, after the taking of the census.
[ 1580-90; lustrum; cf. LUSTER 1 ]