sweetening vs sweeten

sweetening is a noun but sweeten is not a noun.

Word	Noun	Adjective	Verb	Adverb
sweetening	Yes	No	No	No
sweeten	No	No	Yes	No

sweetening (noun)	sweeten (noun)
the act of adding a sweetener to food
an improvement that makes something more agreeable
something added to foods to make them taste sweeter

sweetening (verb)	sweeten (verb)
	make sweeter, more pleasant, or more agreeable
	make sweeter in taste