/ Dictionary / Index I Isth.: Meaning and Definition of Find definitions for: Isth. Pronunciation: [key] isthmus. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. istesso tempo, l' isthmian Related Content Daily Word Quiz: acquiesce Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language