/ Dictionary / Index R reaction engine: Meaning and Definition of Find definitions for: reac'tion en"gine Pronunciation: [key] — Aeron., Rocketry. Aeron.,Rocketry. 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. reactionary reaction formation Related Content Daily Word Quiz: vertigo Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language