Breadcrumb Home > Dictionary > Index F Fourth International: Meaning and Definition of Find definitions for: Fourth' Interna'tional Pronunciation: [key] a loose federation of small groups of radical socialists formed in 1936 under the leadership of Leon Trotsky and hostile to the Soviet Union. Cf.(def. 6). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. fourth estate fourthly ✖ Related Content Daily Word Quiz: hortatory Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language