/ Dictionary / Index O optical activity: Meaning and Definition of Find definitions for: op'tical activ'ity Pronunciation: [key] — Physical Chem. Physical Chem. the ability of a substance to rotate the plane of polarization of plane-polarized light. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. optical optical art Related Content Daily Word Quiz: arboreal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language