third base . third base {n.} The base to be touched third in baseball. He reached third base standing up on a long triple. Categories: add yours {n.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: T Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Leave my opinion