first base . first base {n. phr.} 1. The base that must be touched first by a baseball player after batting. He got to first base on four balls. 2. See: GET TO FIRST BASE. Categories: add yours {n. phr.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: F Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Discuss