Wiktionary
thermionic valve
n. (context now chiefly historical English) An early electronic device incorporating electrons from a glowing cathode inside an evacuated glass tube, functioning as a switch, amplifier etc.
WordNet
thermionic valve
n. electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope [syn: tube, vacuum tube, thermionic vacuum tube, thermionic tube, electron tube]
Usage examples of "thermionic valve".
At the beginning of the twentieth century came the next major developmentthe thermionic valve, or vacuum tube.
But she'd be dipped in dogshit before she'd believe that the disc was built by a thermionic valve technology.