Prussian

region in northeastern Germany, late 14c., Prusse (late 13c. as a surname), from Medieval Latin Borussi, Prusi, Latinized forms of the native name of the Lithuanian people who lived in the bend of the Baltic before being conquered 12c. and exterminated by (mostly) German crusaders who replaced them as the inhabitants.

Perhaps from Slavic *Po-Rus "(Land) Near the Rusi" (i.e. Russians; compare Pomerania). The German duchy of Prussia after the 17c. union with the Mark of Brandenberg became the core of the Prussian monarchy and later the chief state in the German Empire. The center of power shifted to Berlin after the union, and the old core of the state came to be known as East Prussia.

word-forming element meaning "pertaining to," from Latin -anus, adjective suffix, in some cases via French -ain, -en. From PIE *-no-.

word-forming element used in science for the carbon-nitrogen compound radical, from a Latinized form of Greek kyanos "dark blue" (see cyan).

The immediate source of its use in science is French cyanogène, the name given to the compound radical by Gay-Lussac. He called it that because it first had been obtained by heating the dye pigment powder known as Prussian blue (see Prussian).

The cyanogen radical was one of the first examples of a 'compound radical' and was of importance in the development of structural chemistry during the next forty years. [Flood, "Origins of Chemical Names"]