Literally 'easy death,' the act or practice of putting people to death because they or others decide that continued life would be burdensome. Originally the term was used for 'mercy killing,' which meant administration of an easy, painless death to one who was suffering from an incurable and perhaps agonizing disability or disease. Then, as mass genocide was legalized under Communism and Nazism, the term came to ge applied to all forms of inflicting death on persons who are, by legal standards, permitted to take their lives or others are allowed to do so with the full protection of the civil law.
The Holy See was asked, "Is it permissible upon the mandate of public authority, directly to kill those who, although they have committed no crime deserving of death, are yet, because of psychic or physical defects, unable to be useful to the nation, but rather are considered a burden to its vigor and strength?" The reply was No, and the reason given was that "it is contrary to the natural and divine positive law" (Pius XII, Decree of the Holy Office, December 1940).