ion engine

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

• noun A rocket engine that develops thrust by expelling ions rather than gaseous combustion products.

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

• noun astronautics a type of spacecraft propulsion, whereby electric fields accelerate ions out the exhaust to provide motive force

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

• noun a type of reaction-propulsion engine to propel rockets in space; a stream of positive ions is accelerated to a high velocity by an electric field