Merriam-Webster Collegiate Dictionary - heterodyne

 I. adjective  Etymology: heter- + -dyne, modification of Greek dynamis power — more at dynamic  Date: 1908 of or relating to the production of an electrical beat between two radio frequencies of which one usually is that of a received signal-carrying current and the other that of an uninterrupted current introduced into the apparatus; also of or relating to the production of a beat between two optical frequencies  II. transitive verb  (-dyned; -dyning)  Date: 1923 to combine (as a radio frequency) with a different frequency so that a beat is produced