act up vs act

act up is not a noun while act is a noun.

Word	Noun	Adjective	Verb	Adverb
act up	No	No	Yes	No
act	Yes	No	Yes	No

act up (noun)	act (noun)
	something that people do or cause to happen
	a subdivision of a play or opera or ballet
	a legal document codifying the result of deliberations of a committee or society or legislative body
	a short performance that is part of a longer program
	a manifestation of insincerity

act up (verb)	act (verb)
make itself felt as a recurring pain	behave in a certain manner; show a certain behavior; conduct or comport oneself
misbehave badly; act in a silly or improper way	pretend to have certain qualities or state of mind
	discharge one's duties
	play a role or part
	perform on a stage or theater
	behave unnaturally or affectedly
	perform an action, or work out or perform (an action)
	have an effect or outcome; often the one desired or expected
	be suitable for theatrical performance