light up light up {v.} Suddenly to look pleased and happy. Martha's face lit up when she saw her old friend. Tom will really light up when he sees his new bike! Categories: add yours friends {v.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: L Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Post my comment