improver

One who or that which improves.

One who labors at a trade for the purpose of increasing his knowledge or skill, and who accepts the opportunity of improvement as compensation in whole or in part for services rendered.

A pad or cushion worn by women with the object of improving the figure or the hang of a dress; a bustle.

One who, or that which, improves.

Something that, or someone who, improves

A substance added to cause improvement (especially to a foodstuff)

someone devoted to the promotion of human welfare and to social reforms

a component that is added to something to improve it