1) Electronics 
Thermionics is a branch of physics dealing with the emission of ions by hot bodies. The first thermionic observation, though not understood at the time, was made by Thomas Edison, and is known as the Edison effect.
[n] - the branch of electronics dealing with thermionic phenomena (especially thermionic vacuum tubes)
thermionics The study and applications of thermionic emissions, or charged particles, from heated surfaces.
noun the branch of electronics dealing with thermionic phenomena (especially thermionic vacuum tubes)