/ Dictionary / Index C cotter pin: Meaning and Definition of Find definitions for: cot'ter pin" Pronunciation: [key] — Mach. Mach. a cotter having a split end that is spread after being pushed through a hole to prevent it from working loose. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. cotter cotter slot Related Content Daily Word Quiz: pedagogy Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language