Meaning of reaction engine

reac'tion en"gine

Pronunciation: [key]
— Aeron., Rocketry. Aeron.,Rocketry.
  1. an engine that produces power as a reaction to the momentum given to gases ejected from it, as a rocket or jet engine. Also called
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.