/ Dictionary / Index L light chain: Meaning and Definition of Find definitions for: light' chain" Pronunciation: [key] either of an identical pair of polypeptides in the antibody molecule that lie parallel to the upper parts of the heavy chain pair and are half the molecular weight. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. light bulb light colonel Related Content Daily Word Quiz: lunar Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language