an electronic valve having three electrodes, a cathode, an anode, and a grid, the potential of the grid controlling the flow of electrons between the cathode and anode. It has been replaced by the transistor
2.
any electronic device, such as a thyratron, having three electrodes
Word origin
C20: tri- + electrode
triode in American English
(ˈtraɪˌoʊd)
noun
an electronic device with three electrodes; esp., an electron tube with an anode, cathode, and grid