/ Dictionary / Index L Lewis acid: Meaning and Definition of Find definitions for: Lew'is ac'id Pronunciation: [key] — Chem. Chem. any substance capable of forming a covalent bond with a base by accepting a pair of electrons from it. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. lewis Lewis and Harris Related Content Daily Word Quiz: penchant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language