cathode vs cold cathode

cathode and cold cathode both are nouns.

Word	Noun	Adjective	Verb	Adverb
cathode	Yes	No	No	No
cold cathode	Yes	No	No	No

As nouns, cold cathode is a hyponym of cathode; that is, cold cathode is a word with a more specific, narrower meaning than cathode:

cathode: a negatively charged electrode that is the source of electrons entering an electrical device
cold cathode: a cathode that is a source of electrons without being heated

Other hyponyms of cathode include photocathode.

cathode (noun)	cold cathode (noun)
a negatively charged electrode that is the source of electrons entering an electrical device	a cathode that is a source of electrons without being heated
the positively charged terminal of a voltaic cell or storage battery that supplies current