Thomson effect n (General Physics) physics the phenomenon in which a temperature gradient along a metallic (or semiconductor) wire or strip causes an electric potential gradient to form along its length [named after Sir William Thomson, Lord Kelvin]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014