knotty problem . knotty problem {n. phr.} A very complicated and difficult problem to solve. Doing one's income tax properly can present a knotty problem. Categories: add yours {n. phr.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: K Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Post my comment