Hypertext Webster Gateway: "Lustra"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Lustrum \Lus"trum\, n.; pl. E. {Lustrums}, L. {Lustra}. [L. Cf.
2d & 3d {Luster}.]
A lustration or purification, especially the purification of
the whole Roman people, which was made by the censors once in
five years. Hence: A period of five years.
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