terrestrial guidance n (Astronautics) a method of missile or rocket guidance in which the flight path is controlled by reference to the strength and direction of the earth’s gravitational or magnetic field. Compare inertial guidance Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014