tidy sum tidy sum {n. phr.} A large amount of money. The Smith's big new home cost them a tidy sum. Compare: PRETTY PENNY. Categories: add yours {n. phr.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 » In RussianTo section: T Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Comment on this entry