flimsy vs unbelievable

flimsy is a noun but unbelievable is not a noun.

Word	Noun	Adjective	Verb	Adverb
flimsy	Yes	Yes	No	No
unbelievable	No	Yes	No	No

flimsy (noun)	unbelievable (noun)
a thin strong lightweight translucent paper used especially for making carbon copies

flimsy (adjective)	unbelievable (adjective)
not convincing	beyond belief or understanding
lacking solidity or strength	having a probability too low to inspire belief
lacking substance or significance