/ Dictionary / Index B boundary layer: Meaning and Definition of Find definitions for: bound'ary lay"er Pronunciation: [key] — Physics. Physics. the portion of a fluid flowing past a body that is in the immediate vicinity of the body and that has a reduced flow due to the forces of adhesion and viscosity. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. boundary condition boundary line Related Content Daily Word Quiz: sinister Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language