crack-up vs breakdown

crack-up and breakdown both are nouns.

Word	Noun	Adjective	Verb	Adverb
crack-up	Yes	No	No	No
breakdown	Yes	No	No	No

As nouns, crack-up and breakdown are synonyms defined as:

crack-up (noun)	breakdown (noun)
a mental or physical breakdown	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