Definition of "lustrum" [lus•trum]

• A ceremonial purification of the entire ancient Roman population after the census every five years. (noun)
• A period of five years. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Does the Latin word "lustrum" mean a bright light, a century, or a period of five years?"
• "These were the twenty-sixth pair of censors since the first, the lustrum was the nineteenth."
• "And with this in mind, and in the renewed hope that I may live long enough to see the task through, I shall now relate the extraordinary story of Cicero’s year in office as consul of the Roman republic and what befell him in the four years afterward—a span of time we mortals call a lustrum, but which to the gods is no more than the blinking of an eye."