Lustrum

n. period of five years; purification of the Roman people every five years subsequent to census; Roman census

Lustrum was a sacrifice for expiation and purification offered by one of the censors of Rome in name of the Roman people at the close of the taking of the census, and which took place after a period of five years, so that the name came to denote a period of that length. The word also signifies a period of five years.
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Noun
1. a period of five years
(hypernym) time period, period of time, period
2. a ceremonial purification of the Roman population every five years following the census
(hypernym) ceremony
(derivation) lustrate
(classification) antiquity
(classification) Rome, Roma, Eternal City, Italian capital, capital of Italy

n. lustrum

n. lustrum, lustre, luster