undue vs due

undue is not a noun while due is a noun.

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

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

undue (adjective)	due (adjective)
not yet payable	owed and payable immediately or on demand
not appropriate or proper (or even legal) in the circumstances	suitable to or expected in the circumstances
beyond normal limits	capable of being assigned or credited to
lacking justification or authorization	scheduled to arrive

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