/ Dictionary / Index P polonium: Meaning and Definition of Find definitions for: po•lo•ni•um Pronunciation: (pu-lō'nē-um), [key] — n. Chem. a radioactive element discovered by Pierre and Marie Curie in 1898; Symbol: Po; at. no.: 84; at. wt.: about 210. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: polonium (Thesaurus) polonaise Polonius Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language