nice Nelly . nice Nelly (1) or nice Nellie {n.}, {informal} Someone who acts too good to be true; a prude; a prig. We took him for a nice Nelly when he wouldn't fight. Categories: add yours {informal} {n.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: N Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Comment on this entry