U. abbreviation for 1. (Mathematics) maths union 2. unit 3. united 4. (Education) university 5. upper Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014