/ Dictionary / Index S surface boundary layer: Meaning and Definition of Find definitions for: sur'face bound'ary lay"er Pronunciation: [key] — Meteorol. Meteorol. the thin layer of air adjacent to the earth's surface, usually considered to be less than 300 ft. (91 m) high. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. surface-active agent surface condenser Related Content Daily Word Quiz: procrastinate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language