thermionˈic adjective

Of or relating to thermions

thermionˈics singular noun

The science of thermions and thermionic emissions

thermionic emission noun

The emission of electrons from incandescent solids or liquids

thermionic valve or thermionic tube noun

A vacuum tube containing a heated cathode from which electrons are emitted, an anode for collecting some or all of these electrons and, generally, additional electrodes for controlling their flow to the anode