undoing vs undo

undoing is a noun but undo is not a noun.

Word	Noun	Adjective	Verb	Adverb
undoing	Yes	No	No	No
undo	No	No	Yes	No

undoing (noun)	undo (noun)
an act that makes a previous act of no effect (as if not done)
loosening the ties that fasten something

undoing (verb)	undo (verb)
	cancel, annul, or reverse an action or its effect
	cause to become loose
	remove the outer cover or wrapping of
	deprive of certain characteristics
	cause the ruin or downfall of