/ Dictionary / Index A actinide series: Meaning and Definition of Find definitions for: ac'tinide se"ries Pronunciation: [key] — Chem. Chem. the series of radioactive elements that starts with actinium and ends with lawrencium. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. actinide actiniform Related Content Daily Word Quiz: agitated Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language