cleanup vs improvement

cleanup and improvement both are nouns.

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

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

cleanup (noun)	improvement (noun)
the act of making something clean	the act of improving something
(baseball) the fourth position in the batting order (usually filled by the best batter on the team)	a change for the better; progress in development
a very large profit	a condition superior to an earlier condition