hcn

(chemistry) Initialism of hydrogen cyanide. [(inorganic chemistry) A colourless, very poisonous, volatile liquid, HCN, used in the production of dyes, plastics and fumigants; it dissolves in water to form hydrocyanic acid and reacts with bases to form cyanides, and with some organic compounds to form nitriles.]

(numbers) Initialism of highly composite number. [(number theory) A positive integer that has more divisors than any smaller positive integer.]