glow lamp vs gas-discharge tube

glow lamp and gas-discharge tube both are nouns.

Word	Noun	Adjective	Verb	Adverb
glow lamp	Yes	No	No	No
gas-discharge tube	Yes	No	No	No

As nouns, gas-discharge tube is a hypernym of glow lamp; that is, gas-discharge tube is a word with a broader meaning than glow lamp:

glow lamp: a gas-discharge tube with a hot cathode; used in stroboscopes
gas-discharge tube: a tube in which an electric discharge takes place through a gas

glow lamp (noun)	gas-discharge tube (noun)
a gas-discharge tube with a hot cathode; used in stroboscopes	a tube in which an electric discharge takes place through a gas