Definition of improver:
(n) :
Something that, or someone who, improves something.
(n) :
One who improves his or her performance, one who shows improvement (of individuals or groups).
(n) :
A substance added to cause improvement (especially to a foodstuff).
(n) :
One who performs improv; an improviser.
(n) :
(obsolete) Specifically, a person who improves land or property, a landscaper.
(n) :
(historical) A pad worn by women to make the dress hang properly.