build up vs buildup

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

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

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

build up (verb)	buildup (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