reaction engine

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An engine that develops thrust by the focused expulsion of matter, especially ignited fuel gases.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any engine that generates thrust by expelling matter, especially hot gases produced by igniting a fuel; either a rocket engine or several types of jet engine.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a jet or rocket engine based on a form of aerodynamic propulsion in which the vehicle emits a high-speed stream