lus·trum \ˈləstrəm\noun (plurallus·trums \-trəmz\ ; orlus·tra \-trə\) Etymology: Latin; akin to Latin lucēre to shine — more at light 1. a.: a purification of the whole Roman people made in ancient times after the census which was taken every five years b.: the Roman census 2.: a period of five years : quinquennium < from 1797-1802 they shared a lustrum of sympathy and love — George Mallaby >