break up vs breakup

break up is not a noun while breakup is a noun.

Word	Noun	Adjective	Verb	Adverb
break up	No	No	Yes	No
breakup	Yes	No	No	No

break up (noun)	breakup (noun)
	the termination or disintegration of a relationship (between persons or nations)
	coming apart

break up (verb)	breakup (verb)
laugh unrestrainedly
break or cause to break into pieces
come to an end
separate (substances) into constituent elements or parts
cause to go into a solution
cause to separate
close at the end of a session
bring the association of to an end or cause to break up
make a break in
set or keep apart
break violently or noisily; smash
attack with or as if with a pickaxe of ice or rocky ground, for example
release ice
destroy the completeness of a set of related items
take apart into its constituent pieces
suffer a nervous breakdown
disband
to cause to separate and go in different directions
discontinue an association or relation; go different ways