/ Dictionary / Index A ack.: Meaning and Definition of Find definitions for: ack. Pronunciation: [key] acknowledge. acknowledgment. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. -acity ack-ack Related Content Daily Word Quiz: tenacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language