Where does euthanasia come from?

Euthanasia is a mass noun (or noncount noun), that is, a noun used only in the singular form.

The word comes from the Greek euthanatos, which means “easy death.” In English, euthanasia has been used in exactly this sense since the early seventeenth century, when Francis Bacon described the phenomenon as “after the fashion and semblance of a kindly & pleasant sleepe.” Nowadays, the word usually refers to the means of attaining such a death.