The emission of electrons or ions by a hot object. For example, the filament in a mass spectrometer spits out energetic electrons that ionize atoms and molecules in the sample.
Thermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function, of the metal. The charge carriers can be electrons or ions, and in older literature are sometimes referred to as...
discharge of electrons from heated materials, widely used as a source of electrons in conventional electron tubes (e.g., television picture tubes) in ... [8 related articles]
is the boiling off of electrons from heated metals. It gives a source of electrons for cathode ray tubes.
you can get a current to flow from a heated filament to a positive electrode in a vacuum; this emission is simply electrons flowing from the filament to the positive electrode.
electron emission due to thermal agitationelectron emission caused solely by the temperature of the electrodethe emission of electrons from a substance resulting from its elevated temperature
[n] - the emission of electrons from very hot substances
The production of electron emission by thermal means. The first thermionic observation, though not understood at the time, was made by Edison, and is known as the Edison effect. 
thermal emission noun the emission of electrons from very hot substances