/ Dictionary / Index R relative aperture: Meaning and Definition of Find definitions for: rel'ative ap'erture Pronunciation: [key] — Optics. Optics. the ratio of the diameter of a lens, esp. a camera lens, to the focal length; the reciprocal of the f number or focal ratio of the lens. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. relative relative bearing Related Content Daily Word Quiz: diligent Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language