/ Dictionary / Index F fast-breeder reactor: Meaning and Definition of Find definitions for: fast'-breed'er reac"tor Pronunciation: (fast'brē'dur, fäst'-), [key] — Physics. Physics. a breeder reactor in which there is no moderator and fission is caused by high-energy neutrons. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. fast-breaking fast buck Related Content Daily Word Quiz: philtrum Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language