foolproof . foolproof {adj.} So constructed that not even a fool can spoil it; easy. This entrance examination is so easy that it is actually foolproof. Categories: add yours {adj.} 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