cleansing vs improvement

cleansing and improvement both are nouns.

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

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

cleansing (noun)	improvement (noun)
the act of making something clean	the act of improving something
	a change for the better; progress in development
	a condition superior to an earlier condition

cleansing (adjective)	improvement (adjective)
acting like an antiseptic
cleansing the body by washing; especially ritual washing of e.g. hands