U-bend n (Building) a U-shaped bend in a pipe or drain that traps water in the lower part of the U and prevents the escape of noxious fumes or vapours; trap Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014