automatic gain control n (Electronics) control of a radio receiver in which the gain varies inversely with the magnitude of the input, thus maintaining the output at an approximately constant level. Abbreviation: AGC Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014