The story
From Orion + drive, since it originated from Project Orion, a U.S. government study from the 1950s.
Etymology from Wiktionary, CC BY-SA 4.0.
Orion drive
Today it means: A theoretical means to propel spacecraft through space, by detonating nuclear bombs behind the spaceship and riding the nuclear explosions that push against the rear mounted pusher plate. Full definition →