English

Noun

thermionic valve ‎(plural thermionic valves)

1. (now chiefly historical) An early electronic device incorporating electrons from a glowing cathode inside an evacuated glass tube, functioning as a switch, amplifier etc.
   • 2012, George Dyson, Turing's Cathedral, Penguin 2013, p. 65:

     The age of electronics began in 1906 with Lee De Forest's invention of the vacuum tube, or, as the British (led by John Ambrose Fleming, whose work preceded De Forest's) described it, the thermionic valve.

Synonyms

• vacuum tube