the act of killing someone painlessly (especially someone suffering from an incurable illness)
"After years of painful decline, his family made the heartbreaking decision to seek euthanasia to end his suffering."
The practice of intentionally and painlessly killing a human being or animal for humane reasons, especially in order to end great suffering or poor quality of life.
"After months of painful decline from the disease, the family made the heartbreaking decision to pursue euthanasia to spare their dog any further agony."