thermionic tube vs vacuum tube

thermionic tube and vacuum tube both are nouns.

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

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

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

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

thermionic tube (noun)	vacuum 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