To euthanize an animal is to kill it in a planned, painless way, almost always because it is very sick, badly hurt, or so old that life has become cruel. A vet does it with an injection. Families say this when they have to say goodbye to a dog or a cat; shelters say it when they cannot keep an animal alive without more pain. Everyday English also says put down or put to sleep — those sound softer, and children often hear put to sleep first — but euthanize is the clear, adult verb. Though actually, people sometimes use it of humans too, especially in news about the law; many listeners still feel the word belongs first to animals, and using it of a person can sound cold. American spelling is euthanize; British English often writes euthanise. It is not a casual joke-word. If someone uses it lightly about a person they dislike, that is meant to shock.

安樂死（多用於動物）；台灣新聞、收容所也常說「人道毀滅」