breakdown vs crack-up

breakdown and crack-up both are nouns.

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

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

breakdown (noun)	crack-up (noun)
the act of disrupting an established order so it fails to continue	a mental or physical breakdown
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