Source : Webster's Revised Unabridged Dictionary (1913)

Improver \Im*prov"er\, n.
   One who, or that which, improves.

Source : WordNet®

improver
     n 1: someone devoted to the promotion of human welfare and to
          social reforms [syn: {humanitarian}, {do-gooder}]
     2: a component that is added to something to improve it; "the
        addition of a bathroom was a major improvement"; "the
        addition of cinammon improved the flavor" [syn: {addition},
         {add-on}]