/ Dictionary / Index A apostilb: Meaning and Definition of Find definitions for: ap•o•stilb Pronunciation: (ap'u-stilb"), [key] — n. Optics. a unit of luminance equal to one ten thousandth of a lambert. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. apostil apostle Related Content Daily Word Quiz: quandary Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language