/ Dictionary / Index P plane of incidence: Meaning and Definition of Find definitions for: plane' of in'cidence Pronunciation: [key] — Optics. Optics. a plane determined by a given ray, incident on a surface, and the normal at the point where the incident ray strikes the surface. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. plane iron plane polarization Related Content Daily Word Quiz: loathe Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language