/ Dictionary / Index J jack block: Meaning and Definition of Find definitions for: jack' block" Pronunciation: [key] — Naut. Naut. a block used in raising or lowering a topgallant yard. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. jack bean jackboot Related Content Daily Word Quiz: censure Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language