Bringing about gentle and painless death from incurable disease

One word substitute is Euthanasia.

Suicide: the action of killing oneself intentionally.
Euphoria: a feeling or state of intense excitement and happiness.
Gallows: a structure, typically of two uprights and a crosspiece, for the hanging of criminals.
Euthanasia: the painless killing of a patient suffering from an incurable and painful disease or in an irreversible coma.