Pronunciation: (lus'trum), [key]
—pl. -trums, -traPronunciation: (-tru). [key]
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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.