decision tree n a treelike diagram illustrating the choices available to a decision maker, each possible decision and its estimated outcome being shown as a separate branch of the tree Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014