/ Dictionary / Index C cell theory: Meaning and Definition of Find definitions for: cell' the"ory Pronunciation: [key] a basic tenet of modern biology, first stated by Matthias Schleiden and Theodor Schwann in 1838–39, that cells are the basic units of structure and function in living organisms. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. cell sap cellular Related Content Daily Word Quiz: designate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language