/ Dictionary / Index P Prandtl number: Meaning and Definition of Find definitions for: Prand'tl num"ber Pronunciation: (prän'tl), [key] — Physics, Thermodynam. the ratio of the fluid viscosity to the thermal conductivity of a substance, a low number indicating high convection. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. prandial prang Related Content Daily Word Quiz: winsome Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language