act vs make believe

act is a noun but make believe is not a noun.

Word	Noun	Adjective	Verb	Adverb
act	Yes	No	Yes	No
make believe	No	No	Yes	No

As verbs, make believe is a hyponym of act; that is, make believe is a word with a more specific, narrower meaning than act:

act: play a role or part
make believe: represent fictitiously, as in a play, or pretend to be or act like

Other hyponyms of act include make, pretend, support, act out, enact, reenact, act out, impersonate, portray, parody, emote.

act (noun)	make believe (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 (verb)	make believe (verb)
behave in a certain manner; show a certain behavior; conduct or comport oneself	represent fictitiously, as in a play, or pretend to be or act like
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