due vs repayable

due is a noun but repayable is not a noun.

Word	Noun	Adjective	Verb	Adverb
due	Yes	Yes	No	Yes
repayable	No	Yes	No	No

due (noun)	repayable (noun)
that which is deserved or owed
a payment that is due (e.g., as the price of membership)

due (adjective)	repayable (adjective)
owed and payable immediately or on demand	subject to repayment
suitable to or expected in the circumstances
capable of being assigned or credited to
scheduled to arrive

due (adverb)	repayable (adverb)
directly or exactly; straight