/ Dictionary / Index C collision density: Meaning and Definition of Find definitions for: colli'sion den"sity Pronunciation: [key] — Physics. Physics. the rate at which collisions are occurring per unit volume per unit time, usually pertaining to the collisions of neutrons in a nuclear reactor. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. collision course collision diameter Related Content Daily Word Quiz: cautious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language