firebug firebug {n.} An arsonist; one who willfully sets fire to property. The police caught the firebug just as he was about to set another barn ablaze in the country. Categories: add yours {n.} 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