thermionic tube vs electron tube

thermionic tube and electron tube both are nouns.

Word	Noun	Adjective	Verb	Adverb
thermionic tube	Yes	No	No	No
electron tube	Yes	No	No	No

As nouns, thermionic tube and electron tube are synonyms defined as:

thermionic tube and electron tube: electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope

Other synonyms of thermionic tube include thermionic vacuum tube, thermionic valve, tube, vacuum tube.

thermionic tube (noun)	electron tube (noun)
electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope	electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope