1) Addition 2) Annex 3) Annexe 1) Benefactor 2) Do-gooder 3) Emendator 4) Helper 5) Humanitarian 
• (n.) One who, or that which, improves.
Im·prov'er noun One who, or that which, improves. 
improver 1. A person or thing that improves. 2. Someone devoted to the promotion of human welfare and to social reforms. 3. A component that is added to something to improve it.
a person or thing that improves. · a substance or agent added to improve a food, esp. as a preservative.