an electron tube having a cathode electrically heated in order to cause electron or ion emission
Also [Brit., etc.] ; British thermionic valve
thermionic tube in American English
noun
Electronics
a vacuum tube in which the cathode is heated electrically to cause the emission of electronsby thermal agitation
Also called: hot-cathode tube
Word origin
[1925–30]This word is first recorded in the period 1925–30. Other words that entered Englishat around the same time include: distinctive feature, gimmick, payload, reflex camera, turnaround