sweetening vs improvement

sweetening and improvement both are nouns.

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

As nouns, improvement is a hypernym of sweetening; that is, improvement is a word with a broader meaning than sweetening:

sweetening (noun)	improvement (noun)
the act of adding a sweetener to food	the act of improving something
an improvement that makes something more agreeable	a change for the better; progress in development
something added to foods to make them taste sweeter	a condition superior to an earlier condition