/ Dictionary / Index C cerium: Meaning and Definition of Find definitions for: ce•ri•um Pronunciation: (sēr'ē-um), [key] — n. a steel-gray, ductile metallic element of the rare-earth group found only in combination. Symbol: Ce; at. wt.: 140.12; at. no.: 58. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: cerium (Thesaurus) cerise cerium metal Related Content Daily Word Quiz: reclusive Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language