Definition: to make better
From the French “améliorer” which means “improve.”
It seems very similar to “alleviate,” but I read one definition that implied “alleviate” means to reduce suffering, where “ameliorate” means to “make better.” That’s a subtle difference, and I really haven’t seen that reflected in usage (see the example below, for instance).
Why I Looked It Up
In a discussion of the Supreme Court case Adkins vs. Children’s Hospital:
Progressive sought to ameliorate the consequences of industrialization by enacting minimum wage laws.
Regarding the usage note above, you could easily swap “alleviate” in here, and get the same meaning.