/ Dictionary / Index B bulk modulus: Meaning and Definition of Find definitions for: bulk' mod"ulus Pronunciation: [key] — Physics. Physics. a coefficient of elasticity of a substance, expressing the ratio between a pressure that acts to change the volume of the substance and the fractional change in volume produced. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. bulk mail bulky Related Content Daily Word Quiz: fabricate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language