Adjective
designating the acid now called hydrocyanic acid, but formerly called prussic acid, because Prussian blue is derived from it or its compounds. See Hydrocyanic.
Source: Webster's dictionaryFellow critic James Russell Lowell called him "the most discriminating, philosophical, and fearless critic upon imaginative works who has written in America", suggesting—rhetorically—that he occasionally used prussic acid instead of ink. Source: Internet
Cyanide (prussic acid) and nitrate in sorghum crops - managing the risks. Source: Internet