usually daemon, mythology: a supernatural being whose nature is intermediate between that of a god and that of a human being
4
: one that has exceptional enthusiasm, drive, or effectiveness
a demon for work
Doug, putting like a demon, had birdies on the third and sixth … Fred Tupper
5
daemon: a software program or process that runs in the background
A mailer daemon installed on an e-mail system can respond to a piece of incorrectly addressed e-mail by generating an automated message to the sender that the message was undeliverable. J. D. Biersdorfer