noun

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