Noun
a solution of hydrogen cyanide in water; weak solutions are used in fumigating and in the synthesis of organic compounds
Source: WordNetFellow 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