not characteristic of or appropriate to the upper class, especially of Great Britain: certain words and phrases that are considered absolutely non-U.
Origin of non-U
non- + U (adj.)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
adjective British informal
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012