- a colorless poisonous gas, HCN, having a bitter almondlike odor: in aqueous solution it forms hydrocyanic acid.
- a colourless poisonous liquid with a faint odour of bitter almonds, usually made by a catalysed reaction between ammonia, oxygen, and methane. It forms prussic acid in aqueous solution and is used for making plastics and dyes and as a war gas. Formula: HCN
