homeland security n (Government, Politics & Diplomacy) precautions taken by the government of a specified country against terrorist attacks Homeland Security n (Government, Politics & Diplomacy) the United States Department of Homeland Security, the body responsible for dealing with terrorist threats on American soil Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014