/ Dictionary / Index M Marcellus I: Meaning and Definition of Find definitions for: Marcellus I Pronunciation: [key] dieda.d.309, pope 308–309. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Marcellus Marcellus II Related Content Daily Word Quiz: vertigo Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language