potassium cyanide

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An extremely poisonous white compound, KCN, used in the extraction of gold and silver from ores, in electroplating, and in photography, and as a fumigant and insecticide.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun inorganic chemistry The potassium salt of hydrocyanic acid, KCN; the colourless crystals are soluble in water, and it is extremely poisonous, and is used in electroplating, the extraction of gold and silver from their ores, and in photography.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a poisonous salt (KCN) used in electroplating and in photography