thermionic(a = adj.pert) - of or relating to or characteristic of thermions; "thermionic cathode"
Derived form noun thermion₁

thermionic, adj. of or relating to electrons emitted from a substance at very high temperature.

Idiom:
thermionic emission the emission of electrons from a heated source. thermionic valve (US tube) a device giving a flow of thermionic electrons in one direction, used esp. in the rectification of a current and in radio reception.

thermionic current, thermionic emission, thermionic tube, thermionic vacuum tube, thermionic valve