nervous breakdown vs breakdown

nervous breakdown and breakdown both are nouns.

Word	Noun	Adjective	Verb	Adverb
nervous breakdown	Yes	No	No	No
breakdown	Yes	No	No	No

As nouns, breakdown is a hypernym of nervous breakdown; that is, breakdown is a word with a broader meaning than nervous breakdown:

Other hypernyms of nervous breakdown include crack-up.

nervous breakdown (noun)	breakdown (noun)
a severe or incapacitating emotional disorder	the act of disrupting an established order so it fails to continue
	an analysis into mutually exclusive categories
	a cessation of normal operation
	(biology) the process of decay caused by bacterial or fungal action
	(chemistry) separation of a substance into two or more substances that may differ from each other and from the original substance
	a mental or physical breakdown