Here's a breakdown:
* Pejoration is the process where a word's meaning shifts over time to become more negative or derogatory. For example, the word "villain" originally meant "farmer" but now carries a negative connotation.
* Amelioration is the process where a word's meaning shifts over time to become more positive or less negative. For example, the word "nice" originally meant "foolish" or "ignorant," but now it means "pleasant" or "kind."
So, while pejoration makes a word's meaning worse, amelioration makes it better.