buildup vs build up

buildup is a noun but build up is not a noun.

Word	Noun	Adjective	Verb	Adverb
buildup	Yes	No	No	No
build up	No	No	Yes	No

buildup (noun)	build up (noun)
the act of building up an accumulation
highly favorable publicity and praise
the result of the process of accumulation

buildup (verb)	build up (verb)
	form or accumulate steadily
	enlarge, develop, or increase by degrees or in stages
	change the use of and make available or usable
	bolster or strengthen
	prepare oneself for a military confrontation