/ Thesaurus / A Synonyms of atomic number 89 Find synonyms for: Noun1. actinium, Ac, atomic number 89, chemical element, elementusage: a radioactive element of the actinide series; found in uranium oresWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: illegible Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language