improver vs benefactor

improver and benefactor both are nouns.

Word	Noun	Adjective	Verb	Adverb
improver	Yes	No	No	No
benefactor	Yes	No	No	No

As nouns, benefactor is a hypernym of improver; that is, benefactor is a word with a broader meaning than improver:

improver: someone devoted to the promotion of human welfare and to social reforms
benefactor: a person who helps people or institutions (especially with financial help)

Other hypernyms of improver include helper.

improver (noun)	benefactor (noun)
a component that is added to something to improve it	a person who helps people or institutions (especially with financial help)
someone devoted to the promotion of human welfare and to social reforms