/ Dictionary / Index C counter-ion: Meaning and Definition of Find definitions for: coun•ter-i•on Pronunciation: (koun'tur ī"un, -ī"on), [key] — n. Physical Chem. an ion in solution that associates itself with an ion of opposite charge on the surface of a member of a solute. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. counterintuitive counterirritant Related Content Daily Word Quiz: paradox Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language