fer·ro·cyanide I. \“+\noun Etymology: International Scientific Vocabulary ferrocyanic + -ide : a salt of ferrocyanic acid obtained usually by reaction of a cyanide (as calcium cyanide) with ferrous sulfate or by recovery from spent oxide < calcium ferrocyanide Ca2Fe(CN)6 > — see iron blue, prussian blue II. noun : the tetravalent anion Fe(CN)64-