breakdown vs break down

breakdown is a noun but break down is not a noun.

Word	Noun	Adjective	Verb	Adverb
breakdown	Yes	No	No	No
break down	No	No	Yes	No

breakdown (noun)	break down (noun)
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

breakdown (verb)	break down (verb)
	collapse due to fatigue, an illness, or a sudden attack
	stop operating or functioning
	separate (substances) into constituent elements or parts
	make a mathematical, chemical, or grammatical analysis of; break down into components or essential features
	make ineffective
	cause to fall or collapse
	lose control of one's emotions
	fall apart