AUDION

elementary form of radio tube developed in 1906 (patented 1907) by Lee De Forest of the United States. It was the first vacuum tube in which a control grid as well as a cathode and an anode was incorporated. With the development of multigrid tubes in the 1920s, the generic term audion fell into disuse and was replaced by more descriptive terminology. See also triode; tetrode; pentode.