LED vs diode

LED and diode both are nouns.

Word	Noun	Adjective	Verb	Adverb
LED	Yes	No	No	No
diode	Yes	No	No	No

As nouns, diode is a hypernym of LED; that is, diode is a word with a broader meaning than LED:

LED: diode such that light emitted at a p-n junction is proportional to the bias current; color depends on the material used
diode: a semiconductor that consists of a p-n junction

Other hypernyms of LED include crystal rectifier, junction rectifier, semiconductor diode.

LED (noun)	diode (noun)
diode such that light emitted at a p-n junction is proportional to the bias current; color depends on the material used	a semiconductor that consists of a p-n junction
	a thermionic tube having two electrodes; used as a rectifier