/ Dictionary / Index S strontium 90: Meaning and Definition of Find definitions for: strontium 90 Pronunciation: [key] — Chem. Chem. a harmful radioactive isotope of strontium, produced in certain nuclear reactions and present in their fallout. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. strontium strontium hydroxide Related Content Daily Word Quiz: reiterate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language