/ Dictionary / Index C collision diameter: Meaning and Definition of Find definitions for: colli'sion diam"eter Pronunciation: [key] — Physics. Physics. the distance between the centers of two colliding molecules when at their closest point of approach. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. collision density collision insurance 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