the GNU version of the Collaborative International Dictionary of English
n. One who meliorates.
The Century Dictionary and Cyclopedia
n. One who or that which meliorates or makes better.
Word Usage
"With the banks of my meadow ditches, I have greatly enriched my upland fields, those which I intend to rest for a few years, I constantly sow with red clover, which is the greatest meliorator of our lands."