/ Dictionary / Index C clack valve: Meaning and Definition of Find definitions for: clack' valve" Pronunciation: [key] a valve having a hinged flap permitting flow only in the direction in which the flap opens. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Clackmannan Clactonian Related Content Daily Word Quiz: agitated Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language