/ Dictionary / Index U uranium 239: Meaning and Definition of Find definitions for: uranium 239 Pronunciation: [key] — Chem. Chem. the uranium isotope with a mass number 239. It is artificially produced by the neutron bombardment of uranium 238. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. uranium 238 uranium dating Related Content Daily Word Quiz: cacophony Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language