'Improver' definitions:

Definition of 'improver'

From: WordNet
noun
Someone devoted to the promotion of human welfare and to social reforms [syn: humanitarian, do-gooder, improver]
noun
A component that is added to something to improve it; "the addition of a bathroom was a major improvement"; "the addition of cinnamon improved the flavor" [syn: addition, add-on, improver]

Definition of 'Improver'

From: GCIDE
  • Improver \Im*prov"er\, n. One who, or that which, improves. [1913 Webster]