hydrogen cyanide

American  

noun

1. a colorless poisonous gas, HCN, having a bitter almondlike odor: in aqueous solution it forms hydrocyanic acid.

---

hydrogen cyanide British  

noun

1. Also called: 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

---

hydrogen cyanide Scientific  

1. A colorless, flammable, extremely poisonous liquid. Salts derived from it have many industrial uses, such as hardening iron and steel, extracting metals from ores, electroplating metallic surfaces, and making acrylonitrile, from which acrylic fibers and plastics are produced. It is also used to make dyes and poisons. A solution of hydrogen cyanide in water forms a colorless acid called hydrocyanic acid. Chemical formula: HCN.

---

Etymology

Origin of hydrogen cyanide

First recorded in 1880–85

Example Sentences

This toxic smoke can include carbon monoxide and hydrogen cyanide.

From BBC • Mar. 16, 2026

To better understand how reactive this molecule can be, Marco Capelletti, Hilda Sandström and Martin Rahm used computer modeling to study hydrogen cyanide in its frozen state.

From Science Daily • Jan. 16, 2026

The researchers also demonstrated that their laser can effectively detect hydrogen cyanide gas in the air, a substance commonly referred to as "hydrocyanic acid."

From Science Daily • Oct. 19, 2025

Sodium cyanide is also highly soluble in water and it can react vigorously to produce the gas hydrogen cyanide - which is also toxic.

From BBC • Mar. 11, 2025

I checked the air conditioners; they’re still working, and the filters are efficient enough to take care of an awful lot of hydrogen cyanide.

From Unwise Child by Garrett, Randall