1554, from Prussia, from M.L. Borussi, Prusi, Latinized forms of the native name of the Lithuanian people who lived there before being conquered 12c. and exterminated by German crusaders who replaced them. Perhaps from Slavic *Po-Rus "(The Land) Near the Rusi" (Russians). Prussic acid (1790), is from Fr. acide prussique, so called in reference to the prussian blue pigment, to which it is chemically related. Prussian blue (1724) is from Fr. bleu de Prusse, so called for being discovered in Berlin, the Prussian capital, in 1704 by color-maker Heinrich Diesbach.