Cyanide is a very strong poison. In science it is not one bottle with one name: it is a small chemical piece (carbon stuck to nitrogen) that sits inside several compounds — potassium cyanide, sodium cyanide, hydrogen cyanide gas — and those are what people usually mean. A tiny amount can stop the body from using the air it breathes, so it can kill quickly. That is why crime films show a hidden “cyanide pill”: a last, terrible way out. Though actually, cyanide is not only a murder tool. Some mines use cyanide compounds to pull gold out of rock, and factories use them in other work; that is still the same poison, handled with strict rules. Everyday English also stretches the word: people say “cyanide” for any instant, deadly chemical, even when the bottle is something else. The word belongs to news, police stories, and chemistry class. It feels technical and grave, not like chat.