/ Dictionary / Index J jack post: Meaning and Definition of Find definitions for: jack' post" Pronunciation: [key] a post for supporting a floor beam, having two telescoping sections, adjustable to any height. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. jack plane jackpot 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