The Oxford English Dictionary Online (2nd edition, 1989; online version Sep. 2011) provides the following definitions of euthanasia:

“A gentle and easy death… [T]he means of bringing about a gentle and easy death…

In recent use: The action of inducing a gentle and easy death. Used esp. with reference to a proposal that the law should sanction the putting painlessly to death of those suffering from incurable and extremely painful diseases.”

Sep. 2011